Mr Leadfoot, boy am I glad I found this thread. I have a 2020 Denali, 6.2 and 22's, with the EXACT issues you have been describing in 4 pages. To give you some color, back when I purchased brand new, I test drove another color truck, it road fine, but ended up going for a black one with every option available. I am embarrassed to say I didn't test drive the exact truck I purchased. Covid had just hit, everything shut down, they had weird rules about driving trucks, etc. Anyway, on my way home, I noticed shaking as you described. I called with 12 miles on the truck complaining about spending 72k on a truck that rides worse then the 2017 I had just traded. They did a Pico test, replaced tires, and it did improve but never went away. They basically said sorry your truck was within spec on the Pico test after so much back and forth. I was exhausted by the process and said whatever, I am just driving it. I've put different GM wheels on for winter, new tires, etc, my problem has never managed to go away. I just purchased Defenders for my stock wheels a couple of weeks ago, the truck now has 37k on it. They made a HUGE difference, but it still shakes.
With all of that said, I am totally convinced part of the issue is the DFM. I disable autostop every time I get in the truck, but have strongly considered purchasing the DFM disabler. I notice some weird idling at times which leads me to believe its DFM related. The dealership replaced 4 of my injectors at one point because of rough idle, it still shakes. I can't blame the large wheels, my wife has had Audi's with very large wheels and the cars have floated over the roads at any speed. This is my 4th GM in a row, all have been relatively amazing other then this one. I know all brands have annoying quirks, but I ordered a Raptor and should see it by the end of 2023. I still like GM, I just need a change I am so burnt out with this thing. I am not comparing the Raptor to the Denali, two totally different caliber trucks, I am just in desperate need of a change. My advise, trade it before it drives you insane unless you somehow get it lemoned.