You should call the GMC rep directly, not at the dealer but the guy from GMC in Detroit. I had a problem with a Jeep I had bought brand new, and the dealer was screwing me around, so I call the Jeep rep in Detroit and when he came and drove the Jeep, and then he told the service manager to fix that problem TOMORROW! The service guy was panicking because he said "I don't have an opening for tomorrow", so trying to be a nice guy, I told him it didn't have to be fixed tomorrow but next week would be fine, and they fixed the problem. It shouldn't have to come around to you contacting the factory rep because these dealers get paid to fix a warranty problem. The dealer hated me afterword for calling Detroit because it does not look good for them.
Another time I took my 2017 F-150 (with 10,000 miles) to the dealer because I was sitting at a red light one day and the brake pedal went all the way to the floor! What ???. So, I took the truck to the dealership, and they said they could not duplicate the problem. What??? So, I got in the truck, started it up and pushed the brake pedal right to the floor. I told that moron, that ain't supposed to do that. So then, he has one of his mechanics come out to tell me his brand-new F-150 does the same thing. I said bullshit, and walked out to the showroom, found my salesman and said I wanted to test drive a new truck and I could not get it to do that on any of the trucks I test drove that day.
So, I drove out to the Chevy dealer and traded that truck in for a 2018 Silverado 2500 LTZ Duramax, (that truck was a monster) just like that and I will not buy another Ford product! One of the nicest trucks I've ever owned. But I didn't need a diesel because I'm not towing anymore so I bought my current truck, a 2022 GMC AT4, 4x4, 6.2 gas, loaded, with everything except the heads-up display which I really wanted. That was the only truck I could find in stock locally.