The biggest problems were related to the front air suspension, and then a harness that was improperly secured in the transmission tunnel. This is on my 24 Yukon. Within weeks of purchasing the vehicle, the front would lower/sag when sitting overnight. It ended up sitting at the dealer almost a month in total, during which time someone came through one night and broke the windows out on over a dozen vehicles parked on the lot, including mine. it took the dealer 5 days to notify me of this, during which time it continued to sit on their lot, in the rain (they made a half assed attempt to cover it with a flimsy plastic tarp). After meeting with the service manager in person, they finally traced the problem to some module that regulates the front suspension. Essentially, the air in the front shocks was leaking back into the holding tank on the car, which caused the front end to sag.
On the harness, there was a vibration in the transmission tunnel at low RPMs. I dealt with "we don't hear it" or "it's normal" to finally getting them to agree to put the car on a lift and have a tech underneath the vehicle while someone else was inside giving it throttle (with me standing outside the bay watching). At that point, they heard it and agreed that it was not normal, however they couldn't figure out how to fix it. I was by then at my breaking point with this dealer, and decided to try another local GMC dealer. This dealer was quickly able to diagnose the problem and fix it. The way the harness was mounted, it was vibrating directly against the transmission, so once it was remounted properly, the issue went away.
I know these problems may seem trivial. Most of the issues with my 24 Yukon, and previously with my 22 Tahoe, have to do with squeaks, rattles and vibrations (admittedly, my tolerance for these is very low), however the dealers give me subpar service by not providing regular status updates, not returning phone messages or e-mails, giving me inconsistent or downright inaccurate information, etc. There is a consistent rattle on the driver's side b-pillar, a plastic flex/creaking noise in the center dash HVAC panel (where the HVAC buttons are), rattles under both rear seats and a blend door in the rear HVAC that continuously "taps" against the housing at certain temperature settings. Maybe my expectations are too high.