Decided to start a new thread about this... I'd be interested what others experience with this is. There is some more info here:
2020 gmc? any reviews from new owners?
I have a 2020 GMC 3500 Denali that has had the steering wheel shake problem since new. It has the factory 20" rims and Crapyear tires. The truck has now been to two different dealers a total four times for resolution of this issue. It seems to be fairly widespread - I drove 4 other identical trucks, and they all had the issue to some degree. Mine was still the worst. It is most noticeable when is there is slight pressure on either side of steering center, like when correcting for road crown, although even on straight center there is still a discernible shake in the steering wheel.
To date, one tire has been replaced (sidewall bulge, not related), all four tires have been balanced and road forced six times, and the wheels swapped front to rear, side to side, etc. The software update was applied (Bulletin #19-NA-240, N192279900), which helped to some degree, however all it does is increase the steering effort, which masks some of the vibration, and tightens up the centering of the steering box.
GM TAC has told the dealer there is no fix for the problem, and they will no longer pay any more warranty claims on my truck for this issue. They are now saying that this is a "normal" condition. The latest dealer has been great, but they are done, as there is nothing left they can do.
GMC Executive Care team has been working with both me and the dealer to try to figure something out. I was contacted yesterday and informed that GM engineering is working "overtime" on finding both the cause and the fix.
They have determined that although some tires minimize the issue, it is NOT a tire problem that is causing it, and replacing the tires does not represent either a true fix, or a long term solution. I'm not going to dispute that many have found this to work - just relaying what GM has told me.
I take all this to mean that there is a unsprung weight issue with the 20" wheel / tire combo, there is an inherent balance flaw in the stock 20" rims, or a problem with geometry within the steering/ suspension on the Denali and High Country models. The steering wheel shake is not affecting the ATs with 18" wheels.
Ultimately, I have concerns that GM can't fix this issue, and more so what the long term damage may be to the steering and front suspension because of the constant vibration. I love this truck, but when my hands were literally shaking after a 300 mile drive because of the constant vibration, I think its about time to think about other options.