Let me add, that two of my cousins (they are brothers) ordered GMC AT4's with the 3.0 also. It took well over a year for them to get their trucks. Originally, the dealership told them the price would not raise on their new trucks if there was a delay, and also the trade value of the trucks they were trading in would not decline from what the dealer said they would give them for their trucks when they agreed to do the deal and order new trucks through that dealer.
The price on the new trucks stayed the same, but the dealer said they had no choice but to lower the trade value of the trucks they traded in. I mean, it was over a year later and I assume 15K miles or more per truck of use was added in that timeframe. I think they both got about 5K less on trade, even though the dealer originally had promised to not lower their trade value.
It sounds like this is common practice now if you order and trade, if you don't trade in the vehicle right at the time of order, expect your trade value to decline. It's just that they were told and promised that wouldn't happen, but then it did.
Sounds like they like their new trucks, but are unhappy with the very long wait to get them and losing that much trade value. Said they will never order one again that way.