I think it's funny how people think GM trucks are the only ones with issues.. Switching brands isn't always the answer. I can see how people get feed up with GM and switch because of that, but just be careful cause fords and dodges both have their own issues, and similar ones too.
But in regards to the post, my 2015 6.2L 8spd shifts pretty well. When I first got it and it was learning my driving it was definitely annoying and I actually had the dealership reset the tranny once. But after that it's been fine. There are hard downshifts here and there, mostly random, but nothing that shakes the whole vehicle. I also tuned my ECM with the Diablo intune i2 and it made the whole truck drive so much smoother. Can't wait till Diablo offers support for the TCM of the 8spds