I'm here for the same reason, looking for information about this weird happening. Mine is a 16' LTZ, 109,000, bought new. If I drive aggressively? no issues. Drive it like granny? it's all about 5th gear, it doesn't know what to do, where to shift. It's definitely not slipping. I pull it to manual shift and go through the gears with the button it hits hard, no hesitation. drive it easy? I get that jerky sht in 5th at like 40mph.
In the old days I'd say it acts like a bad vacuum modulator. But last time I was inside a trans was in the 80's when it was simple. Clutch plates, bands, worn cluster drums and seals and piston springs. Today it must be black magic - everyone so far says "Oh we need to put a reman in it with a warranty, no one goes inside them anymore. 4 to 5 grand, have you in and out in no time" .... Oh, how nice of you.
If nothing else, I'm almost comforted by finding others with the exact same description. I had an 06' Impala before this one, well had a Taurus Limited in between, but that Impala I put 200K on it, bought it new also, and sold it to the guy who maintains my stuff. He buys all my used ones because he knows them from day 1 and does all the work on them. That car is still going, over 350K last I knew. They did put an engine in it, rod went through the block around 250K miles. Probably their fault.
This MAY help: https://static.nhtsa.gov/odi/tsbs/2020/MC-10173387-9999.pdf