Calling all 6.6l Gas AT4's

[DenaliCountry]

Hi all - new member here. I have been on the hunt for a 2024 AT4 or Denali - 2500HD or 3500HD SRW. I was originally dead set on buying a Duramax, but thinking about switching over to the gasser. I have a few things I tow which is what is pushing me toward a HD truck. I have a bumper pull camper at about 7500lbs, Enclosed snowmobile trailer at about 5K fully loaded and a boat that is in the 6K range. The sleds get hauled the most frequently in the winter and the camper is on the edge of vehicle limits on my current tow vehicle especially if I load the family in with me (2022 Yukon Denali with the 6.2l, Max Tow and Air Ride). Most of my time will be spent on short trips and then every couple weeks to and from our soon to be cabin 100 miles away.

I have had a couple Diesels in the past (LLY and LML) but that was years ago. I remember the LML didn't love city type driving so thinking the newer Duramax engines are probably still similar. All that said, for those that went with the gasser, how are you liking your decision? I told myself I had to have the diesel but the more I think about it, I don't really need it and at a $10K premium I want to make sure I don't over shoot the mark. That said, I also don't want to regret my decision.

As for 2500 VS 3500, I don't see much of a difference in going to the 3500. Tabs in MN on 1 ton's are $120 a year VS the 2500 where I am guessing it will be about $1000/year. Given everything I have read, almost all say get the 1 ton.

Appreciate your input.

 

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[Admin]

Welcome to the forum DenaliCountry! It's a tough decision between the gas and diesel versions, as they both have their advantages. The power and range in the diesel has always been more of a benefit to me, but with that comes extra maintenance cost, and of course a higher starting price. If I didn't tow much, I would probably lean more towards the gas engine.

 

[DenaliCountry]

Welcome to the forum DenaliCountry! It's a tough decision between the gas and diesel versions, as they both have their advantages. The power and range in the diesel has always been more of a benefit to me, but with that comes extra maintenance cost, and of course a higher starting price. If I didn't tow much, I would probably lean more towards the gas engine.

I have similar concerns, the diesel is obviously a beast, I just don't know that I need it with all of the short trips it will make 75% of the time. Are the emissions systems on the new diesels still finicky with short trips? I put on about 10-12K miles a year so the pretty average commuter but most of what I am doing has less than 3-4 miles of highway driving on any given trip.

 

[Mag]

I have had gas engines on all of my previous 2500HD's and the last 2 1500's I've had, including my new '23 AT4 1500. I have a very similar drive situation as you do. About 12,000 miles per year, with more city and slow county back road driving than Interstate. I also just cant justify the added expense of the Diesel engine. The ones I have driven are seriously impressive but I always come back to the $$$ in the end, lol. In fact, at my families 2 store John Deere dealership, we run 2500HD's and 3500HD's all with the older 6.0L or the new 6.6L gas. Ages 2023 to our oldest 2002. These gas engines, while not that efficient, have been bulletproof reliable. I'd say take the gas engine.

 

[DenaliCountry]

I have had gas engines on all of my previous 2500HD's and the last 2 1500's I've had, including my new '23 AT4 1500. I have a very similar drive situation as you do. About 12,000 miles per year, with more city and slow county back road driving than Interstate. I also just cant justify the added expense of the Diesel engine. The ones I have driven are seriously impressive but I always come back to the $$$ in the end, lol. In fact, at my families 2 store John Deere dealership, we run 2500HD's and 3500HD's all with the older 6.0L or the new 6.6L gas. Ages 2023 to our oldest 2002. These gas engines, while not that efficient, have been bulletproof reliable. I'd say take the gas engine.

Thank you! This is very helpful. I am pretty sold on going with the gas engine.

 

[Mag]

Thank you! This is very helpful. I am pretty sold on going with the gas engine.

Just to add a little more info for you. The new 6.6L gas definitely shows some performance increases over the old 6.0L. Most notably in the torque department. It's practically as strong as the 6.2L in the 1/2 tons but with the cast iron lower end and 6 bolt main bearing caps.

 

[DenaliCountry]

Just to add a little more info for you. The new 6.6L gas definitely shows some performance increases over the old 6.0L. Most notably in the torque department. It's practically as strong as the 6.2L in the 1/2 tons but with the cast iron lower end and 6 bolt main bearing caps.

Do the 3500's gasser's come with the 12" rear end?

 

[Mag]

Do the 3500's gasser's come with the 12" rear end?

Good question? I'm not sure to be honest. I know they only run a 3.73 rear end ratio now. The old 6.0L gas you could get with a 3.73 rear or 4.10.

 

[MakerMetals]

Hey thought I would chime in, I have the 1500 with the 3.0L Baby Duramax and LOVE IT, I tow probably every other week, our travel trailer is lighter than yours at 5k but heres some of the stats, we live in a small mountain town with almost no flats, im getting 22mpg in town and 29mpg hwy at 65 and 27mpg at 70mpg, towing the travel trailer with hills getting 15-16 MPG. Truck uses almost no DEF unless towing, then it guzzles it! I couldn't be more happy with the towing and mpg and power. I regularly tow a dump trailer with 4 yards of gravel (10k lbs ish) with it in town and get like 10mpg but it tows awesome. Food for thought.

 

[Teegunn]

Have not had a 3/4 diesel, but did have a 3/4 gas Dodge Ram in the early 2000's. That is so long ago, it is not really relevant.

I am a contractor and always used 1/2 ton's even though I tow regularly. I had a 2020 AT4 3.0 diesel, and loved the engine and truck. It was quick and quiet as a daily driver, and pulled my job trailer (normally aroun 7 to 8 K lbs) well. I did have a bit larger tires and wheels, plus a front level and air bags in the rear for helping with towing. My MPG while driving was around 20 mpg with that setup. My MPG while towing was probably around 8 to 10 on the hwy, and 12ish overall in town. I do live in Montana so have lot's of inclines and hills to traverse. Also live at 6200 ft and that effects MPG.

As I said, I loved everything about the 3.0 AT4 I had, but early last Dec 2022, I had a "service emissons system" code/light come up on my truck. I was out of state working at the time, but the dealership where I was working did the warranty work on it. After a month having the truck, they never could get it figured out and fixed. I was already out of state working for 3 weeks, then adding on 4 extra weeks with my truck in the dealership with this issue, I HAD to be able to drive back home (a 1000 mile trip). That dealership had no other new trucks that were similar level (no AT4's or Chevy ZRr's), and I wasn't willing to trade my truck for a downgrade version.

Luckily they had a new 2023 AT4X come off the semi on Jan 4th 2023, I made the deal for that truck, trading in my 2020 AT4, that same day. The 23 AT4X has the 6.2 gas engine. As I stated, I really liked my 3.0 baby diesel in my 2020 AT4, but any modern diesel has a much more complicated emissions system than a gas truck. And for that reason, I ended up having to trade my 2020 AT4, which I was not considering trading or getting out of at all until this issue happened, for my 23 AT4X.

I like my 23 AT4X better. The fuel MPG difference is probably a wash $ wise for me given that diesel is more expensive than gas. The 6.2 is snappier (as it should be) than the 3.0 diesel, but that little diesel was no dog at all. Towing I would call it a wash - both tow well.

The biggest downfall of the 6.2 gasser vs the 3.0 diesel is the range. With only a 24 gallon tank, the 6.2 gets me about 350 miles down the road on the interstate. The 3.0 diesel would get me 500. I once got 600 miles on one tank (was going mostly downhill and in easy driving following people so wind resistance was nil). That is my main gripe with the 6.2 gas engine - GM should have put at least a 28 gallon tank in this truck.

I will probably never go back to a diesel. My wife still has her 2020 AT4 Carbon Pro 3.0 diesel, and knock on wood, has had no issues at 35K miles and now a little over 3 years. But hers is a driver only, mine was a driver and work truck, so different usage, which could make a difference.

That is my experience and input on gas vs diesel. Not an apples to apples comparison for you, but given what your usage seems to be, I think the 6.6 gas would be just fine for you. The diesel will pull far more with more range, but always a risk of more issues with modern DEF and emissions systems, plus overall higher maintenance costs.

 

[Mag]

Hey thought I would chime in, I have the 1500 with the 3.0L Baby Duramax and LOVE IT, I tow probably every other week, our travel trailer is lighter than yours at 5k but heres some of the stats, we live in a small mountain town with almost no flats, im getting 22mpg in town and 29mpg hwy at 65 and 27mpg at 70mpg, towing the travel trailer with hills getting 15-16 MPG. Truck uses almost no DEF unless towing, then it guzzles it! I couldn't be more happy with the towing and mpg and power. I regularly tow a dump trailer with 4 yards of gravel (10k lbs ish) with it in town and get like 10mpg but it tows awesome. Food for thought.

That's some pretty impressive mpg stats! Others that I have spoken with who have the 6 cyl. Duramax have had similar comments on the mpg and performance. Truthfully, it a lot better mpg than the 6.6L Duramax in the HD's. I wish my 6.2L gas had #'s just a little closer to yours, lol. Do you notice any lag or sluggish start when accelerating empty or with a trailer?

 

[MakerMetals]

That's some pretty impressive mpg stats! Others that I have spoken with who have the 6 cyl. Duramax have had similar comments on the mpg and performance. Truthfully, it a lot better mpg than the 6.6L Duramax in the HD's. I wish my 6.2L gas had #'s just a little closer to yours, lol. Do you notice any lag or sluggish start when accelerating empty or with a trailer?

I don't, the truck is ready to go and towing up to probably 6k total you can drive any speed you want, thats right where it really starts to be noticeable your towing. I tow enough that a truck like this was a need retiring our f350. But I am getting better gas milage not towing than my 2013 tacoma 2wd 4cyl lol. It for sure does not have the face melting power of the 6.6L but if you dont have to have that, this things awesome. If I had to move a mini ex or skid steer regularly then yea go big boy but if its 8-9k lbs here and there and mostly towing 6-7K this thing should for sure be in the top runnings in my opinion.

 

[DenaliCountry]

Hey thought I would chime in, I have the 1500 with the 3.0L Baby Duramax and LOVE IT, I tow probably every other week, our travel trailer is lighter than yours at 5k but heres some of the stats, we live in a small mountain town with almost no flats, im getting 22mpg in town and 29mpg hwy at 65 and 27mpg at 70mpg, towing the travel trailer with hills getting 15-16 MPG. Truck uses almost no DEF unless towing, then it guzzles it! I couldn't be more happy with the towing and mpg and power. I regularly tow a dump trailer with 4 yards of gravel (10k lbs ish) with it in town and get like 10mpg but it tows awesome. Food for thought.

Thank you, I have considered the baby duramax. Problem is the Denali Ultimate, which is the route I would go, only gets me an additional 8-900lbs of additional towing capacity (with no air ride) and similar payload capacity. Payload is where I run out of room quickly with our Travel Trailer. The Yukon tows it fine empty with just me in the car. With me, my wife and 2 kids, the TT hooked up I am only about 4-500lbs away from max payload and that assumes the TT and vehicle are empty.

 

[Mag]

I don't, the truck is ready to go and towing up to probably 6k total you can drive any speed you want, thats right where it really starts to be noticeable your towing. I tow enough that a truck like this was a need retiring our f350. But I am getting better gas milage not towing than my 2013 tacoma 2wd 4cyl lol. It for sure does not have the face melting power of the 6.6L but if you dont have to have that, this things awesome. If I had to move a mini ex or skid steer regularly then yea go big boy but if its 8-9k lbs here and there and mostly towing 6-7K this thing should for sure be in the top runnings in my opinion.

That's great feedback! Sounds like It's one of the few small diesel engines that's got a combo of great performance and great MPG. I have run hi test gas in my previous 1500 Denali and this new 1500 AT4 as is recommended. Certainly that can get $$$ with fuel prices and the marginal mpg I get. I seriously contemplated the Duramax when I ordered this AT4. When we ordered my wife's Z71 Tahoe I thought about it but I don't think it was available for the model Tahoe. Good luck!!

 

[Teegunn]

That's great feedback! Sounds like It's one of the few small diesel engines that's got a combo of great performance and great MPG. I have run hi test gas in my previous 1500 Denali and this new 1500 AT4 as is recommended. Certainly that can get $$$ with fuel prices and the marginal mpg I get. I seriously contemplated the Duramax when I ordered this AT4. When we ordered my wife's Z71 Tahoe I thought about it but I don't think it was available for the model Tahoe. Good luck!!

Having owned an AT4 with the 3.0 diesel, and now a 23 AT4X with the 6.2, I can say that the 3.0 diesel is a fine engine. It averages 5 or so better MPG for my usage and setup on my trucks than the 6.2. The 3.0 is snappy, really quiet for a diesel, and pulls very well.

Now that I have an AT4X with the 6.2, I can compare. I really like the 6.2. It avgs about 15 to 16 mpg just using the truck as a driver. Given that diesel is about 50 cents more expensive than gas, it works out about the same $ wise at the fuel pump overall. The diesel has much better range on the 24 gallon tanks both trucks have - advantage to the diesel here.

The 6.2 is definitely faster/quicker and more powerful for driving. But the 3.0 is not a dog and is no slouch - it is a quick engine to drive. I rarely step into my 6.2, so it is a moot point 99.9% of the time. Towing power is about the same for me as a contractor who pulls job trailers. As it should be, both engines have the same torque.

I wouldn't go back to the 3.0 diesel just because I had to trade mine off because the complicated emissions system ended up stranding me for a month out of state with the dealership unable to fix it. So I have lost trust in modern diesels with complicated emissions systems - I think they are prone to problems sooner or later. The 6.2 could have lifter problems, which is that engines main issue as far as I know. I expect to own my 23 AT4X for another 3 years or so before trading it off, and that will put it between 70K and 90K miles, so hopefully I don't have the 6.2 lifter issue between now and then.

Both engines are nice. I would have not traded off my 2020 AT4 3.0 if it were not for the emissions system problems that GM couldn't fix for me. It more than did the job for me. I do really like the 6.2 though, just wish GM had put a bigger gas tank in the truck.