It will come back. We've been going through this for 2 years now. Finally got them to work with us and I believe they now want to replace the torque converter. It's still at the dealer for the 3rd time for this same problem. The flush "fix" was temporary.Got our 19 traverse With 14,000miles back from dealer. They immediately were able to replicate the shuddering from a stop. So they flushed the trans and filled with a new/different fluid. There is a bulletin from gm about this apparently.
Ous 2018 is at dealer now and they want to replace the torque converter. I pray this is the fix because I really love the car, but it's un-drivable with that shudder!Yes, ours is fixed after replacing torque converter, now it's smooth as butter, shifts nice, not a single shudder on any gears. Drove about 20k after replacement already, so far so good.