I have a 2017 Denali with the 6.2 and 8 speed. I bought it used at 41k, now has almost 160k on it. I have AFM tuned off, I've only used 5w-30 full synthetic since my ownership every 5k, and I really don't mind the 8 speed trans. I did the dipstick retrofit and it was super easy and worth the $$.
I would agree with a lot of the above statements about gadgets and gizmos that can fail. Road manners are great, just avoid the 22 inch wheels - look nice but I hate them for the ride on bad roads.
I'm not a fan of electric steering and a vacuum brake assist pump (this can be deleted BTW). But, both systems work well. The DIY is limited to basic maintenance and repairs, not much you can do computer wise without a subscription.
I have a 2008 6.2 Denali as well and would buy that again no sweat. Your 2006 is the last run of a good generation, so that is something to consider if it's rust free. But, I totally understand the wanting something newer/change it up routine.
I won't buy anything 2021 and newer. I will probably look for a 2017-20 unit in a couple years to update the wife's ride and I'll take the high mileage 2017 and run it some more.
Maintenance on these is key, more so than older generations. But, fluids and filters are cheap in the long run. The 2017 with 84k has a lot of life left in it.......I'd buy that one. It'd be like trading in an old lady for one half her age