STEERMTD

Hi, I have a GMC Savanah with a 6.0L engine and a 6L90 transmission. Purchase brand new in September 2019. In November 2019 we contacted the dealer with 1000 miles on the vehicle about a shutter or hesitation at lower speeds, especially going up hill. It has been to 4 dealers since, and no solution. 17K miles on it. The only thing was at dealer 3, he changed the torque converter. Now it shifts a little different, or it did in the beginning. We are at a loss. GM did extend the bumper to bumper 1 year, so September that's over. I really don't know what the solution is. Get rid of it and purchase a new one? Other than this problem it's perfect for us. Dealer 4 has it now, he cannot find anything wrong. It's crazy really. No codes, ever!