I’m in Chevy sales so, FWIW, although I haven’t owned them myself long-term, I’ve had more than a test drive behind the wheel of the new Tahoes and Suburbans.
The 10-speed is the transmission you want. If you’re looking at a slightly older Tahoe, avoid the 8-speeds. Heard nothing but issues from our techs about them and it’s very obvious when a Colorado or older half ton has one as well, as they’re clunky and awful the majority of the time.
We’ve had a couple of teething issues on the new models, mainly with regards to electronics. The infotainment systems have had some issues with the screen randomly turning off if you give it a bit too much to do at once. XM radio sometimes needs some fiddling to actually connect. Wireless Apple CarPlay doesn’t work well at all and many of my coworkers have all had the same issues with their iPhones over wireless CarPlay (stutters in playback, mainly).
I can’t say that the IRS would be a deciding factor between the two for me, but the new trucks are certainly more refined and pillowy. The interior materials are nicer, the larger infotainment screen is nicer, and everything is just slightly nicer in them. No more ugly steering column shifter either!
I have only seen a select handful of trucks with the new fuel management systems have issues. If they do, a decent GM technician can tear apart your heads and get the engine back together in maybe 5 hours maximum. These are direct-injected, so that comes with its own maintenance, which you should do.
The new Tahoe/Burb has a vastly improved camera system that helps parking a lot. The new ones also have a higher hood line, higher window line, and are generally a little bit harder to park and see smaller cars out of. You get used to it, but I personally feel that the blind spots are worse because of how much taller the truck is/feels.
Good luck on your purchase! Neither is a bad truck and should last you a long time.