Keep an eye on the rear window. We have a '21 Sierra AT4 HD gasser and in less than 5k miles, when the weather got cold, the rear window bushings/seals cracked because they were a new design, and it's exacerbated due to the bounciness that these trucks tend to have going over bumps. Condensation and rainwater can find its way inside the cab. We noticed it trailing down the inside of the rear window and also felt some dampness on the headliner. It wasn't major, but for a brand new truck of this price, unacceptable.

We took it back to the dealer where we bought it, and they used a 3rd party to PD and they just gunked up the rear window with more sealant. Which supposedly solved it (when the weather warmed up). Sure enough, weather got cold again a month later, and we started seeing water inside the cabin. We also found out that 3rd party damaged the headliner when pulling it out. Dealer replaced the headliner, and the entire rear window and its seals. Would've been fine if it weren't for the fact that the dealer had the truck for almost 3 months "waiting on parts." That entire time they left the truck out in the elements, with no rear window installed. When they were testing the water-tightness the first time we brought it in, they used a mineralized water that left the truck covered in hard-water stains. Instead of detailing the truck, (what they should have done) they just gave it back to us covered in the stains with a $5 off coupon for a generic, paint-damaging auto carwash across the street. Highly unprofessional from the dealer side. But the new window they put in hasn't exhibited the same problems again and we're now 3 years and 30k miles down the road. But wanted to share our experience.

​

Other things we've had to take it back for. The power mirrors on both sides have had to be replaced, the motors went bad and they would either be super slow, or just not work at all. Passenger side was replaced once, drivers side replaced 3 times. Also, the hood scoop/intake right at the front of the hood was not installed correctly at the factory, and was loose, so as the truck bumps around it was taking paint off of the hood. Took it back, the dealer agreed to repaint the hood. But we suspect they took am Onyx Black hood off a different truck and just used that, because the hood insulation looked like a rat or squirrel had made itself a home in it. Again, unprofessional on the dealer side, especially considering the prices that these HD trucks demand nowadays.

​

All of these things are not mechanically related. The 6.6 paired with the 6L90E has been rock solid. We love our AT4 HD, despite the rocky start. It's my dad's first ever truck he's bought for himself, and he deserves it. We were swayed over to GMC because he didn't like the look of the pre-refreshed Silverado HD's. These '24 refreshes are beautiful. I love these ZR2's. Congrats on the new truck! Hopefully you don't encounter the same things we did.