I drive a 17 owned by the company I work for and have noticed the same thing
it's very irritating
no wonder GM had to get bailed out by the fedgov
I have not taken it in for repairs because I know GM is too stupid to be able to fix it
I figured it was something to do with the CAFE ratings , it's really irritating that this stupid truck will up shift into 6th gear doing 35 mph uphill
so that when go up the next slight hill in a residential neighborhood mashing the gas pedal does nothing to increase power until you totally floor it causing it to slam down into 3rd and take off like a rocket , there is no way to accelerate in between these two modes unless you drive it in the Manual mode and shift it your self
Using the trailer tow mode helps but the "grade braking " slamming down gears every time you ease off the gas pedal is irritating too
Lexus had rev matching downshifts about ten years ago and GM can't do it ??
it's also hard to believe that they sell a vehicle without power mirrors
and if you don't buy the option package with the remote control to lock and unlock the doors GM has purposely written the software so it can never be added later
The previous company i worked for had crewmax tundras and wow, that's the truck to have . Plenty of power and a very intuitive transmission , rides a hell of a lot better too