Ok, I have a 17 3500 chassy cab savana with a reading box,l96 and 6l90. I have the same exact issue since new 40k miles ago. Even with the other member saying in hotter air temps it worse. Even the weird up shifts. My 15 1500 5.3 seirra does this but it's almost un noticable...almost..
I have a Diablo t1000 tunner I use as a gauge pod in the savana. When this issue is happening the ignition timming is low in the. Single digits and fuel trims sometimes go to near 10% negative and positive. Usualy not the 20%full swing.. No knock retard on the gauge. I was thinking its fuel /ignition related...when its runs good. I see great timming and only a 4 to 6 % swing in fuel trims. And no hesitation. The dealer said it was the torque converter slipping in and out 'as designed'. Well he was wrong. He did a live test scan when I was driving and it was in a solid lock up with zero slip while it was happening. Then he had no other comment on the hesitation feeling. Black bear tunning is my next step. They will do a data log and make a tune for the savanna since there is none out there.
Anyone have any other updates?