About three months ago I noticed the hesitation in shifting. I put five or six gas treatments, thinking it was possibly bad gasoline. I noticed more hard shifting in the lower speed, and about a month later I noticed vibrations. I took it in and thought the tires were out of balance, this didn't help. The vibration has gotten worse, it sounds like you are driving on a rumble strips when you are driving on the highway. It will buck and shifts when it's not supposed to.

I really hope all this works out for us.

Same issue I had with my 2017 Colorado. Shutter/shake when accelerating between 1 & 2. Issue started around 64k miles. Thought maybe it needed the same transmission flush to the newer fluid. Dealer called after 4 days of holding my vehicle (with no loaner or rental option) to tell me that the trans needed an "update" and that it would cost me over $500 since I was over warranty at 67k. There's already a bulletin for the Camshaft Position Actuator Magnet Replacement, which supposedly mimics the same issue. However the dealership says "that's not the problem". I'm sure the same trans issue with hard gear shifts is probably related to this issue now. I haven't felt the hard gear shift in a while but it would do it randomly when accelerating out of my driveway.