I have 101k on my Avalanche (GMT800, same crap), and thinking about selling it
Hasn't failed me yet, and I routinely tow over capacity, load it down, pound it offroad in the desert, and cruise at top speed for stupidly long stretches. They're really cheap to work on if anything does go wrong and very simple. Everything is out in the open. You just have to make sure to flush the trans / 4wd transfer case / diff oil every 15-30k. That's the one thing people neglect and results in failures.
Are you towing big? If so make sure to get the 4.10 gears.