Avoid 16-17 years 6.2 like the plague....
8 speed trans is JUNK!!!!!
2015 early Esky and Denali had 6.2 with 6 speed... tried and true...
2018 is first year or 10 speed behind the 6.2.... great piece
Tahoes and Suburbans also got the 6.2 in the premier trim, sometimes you will find a RST with 6.2 and not premier... But most are premier, the premier package was the LTZ package rebranded.
Mag ride in the 18 and up was corrected for its software issues and harsh ride. The shocks tend to die at 80 k miles... Im at 80k and I can vouch for it... Mine need replacing.
The 40k budget, thats tight for sure for what you want... I may suggest waiting for the bubble to pop the end of the year into early 23, everything I am seeing the used and new markets are about to tank. But if you need it now, shop shop shop wisely. A few dents may be in order to get something with stellar driveline and interior...
Hope your search goes well man... Keep us posted on what you get.