You must’ve gotten a defective rental. I’ve experienced none of that in 4 or 5 new 1/2 ton Silverados, 6,8 or 10 speed. 5.3 or Dmax.
My 2019 Silverado had a 5.3 and a 6-speed. It was often slow to choose a gear. There was a place along my morning drive where it always happened at the end of a straight with a decent left hand curve at the base of an incline. It took some time for it to choose the right gear. On twisty canyon roads it got confused and took too long to shift. I would use ‘manual’ in those situations and just keep it in a specific gear.
The displacement on demand was also not the greatest, but not a huge deal either. One of the main reasons I got rid of it from a mechanical standpoint, is direct injection. At the time, my wife also had a 2017 Honda fit that we’d had since new. It had many issues that had to be handled under warranty related to direct injection. They needed to media blast the intake valves and replace all four injectors before we sold it at 60,000 or so miles.
The more I researched DI, the less I wanted to keep the truck. Given the timing, I was able to sell it with 25,000 miles for more than I paid for it new.