I had a '15 6.2L and absolutely hated the transmission. When I first got the truck, I had no issues at all.. took it in for an oil change and they had some kind of "service update" - They SAID it was just changing out a harness or something... but from that day on, it was a piece of shit. Had it flushed twice and a new TC installed.. nothing helped. I bitched about it every time I took it in for service, and the Service write was just like "yeah, everyone says the same thing" - It was at that point that I knew it was never going to get any better and it was one of the reasons I traded it in on an '18 Denali - and so far, the transmission has been awesome.. none of the other transmission issues the '15 had.