I have a 2017 silverado with the 6.2. I have 4k miles on it.
The tranny can be a little clunky on the downshift, and upshift with light acceleration, in the first couple of gears. The 8 speed with the 6.2 on the highway is absolutely fantastic. An incredible improvement over my 2011, on the highway. I get 22-23 mpgs on the highway running premium shell gas. the lifetime gas mileage is 20 mpg. Not bad for a 4x4 crew cab.
I have the range afm disabler on my '17 and it does improve the driving experience. No drone, better throttle response and no v4 lag. Haven't sacrificed and fuel economy, as far as I can tell. Best mod you can do, IMO.
My last truck was a 2011 silverado with the 5.3 and 6 speed. I experienced the same kind of "clunky" shifts on it as well. I'll also note I traded that one in with about 100k miles on it with no issues. I got 15 mpg in city and on the highway.