I've been having this problem since the end of the summer. Had my tranny 4L60E tranny rebuilt in May and it worked fine all summer. End of summer i would start to get hesitation in the RPM's right after it shifted into 4th gear when cruisin, like going into 35mph or 45-45mph. Revs bounce up and down for a sec or two. It would only noticeably do this when the car was warm.

Tranny place fixed the tourque converter and the leak and said it should fix it, it didnt. They couldn't really pinpoint it. THey say now that PCM needs to be flashed or its a hangin valve in the tranny.
I havent been back to them because I have been busy, but they were going to take the tranny out and check the valve to see if it's the culprit.

Now, i guess since its almost winter it doesn't do that exact thing anymore. When it shifts into 4th now, it takes a sec to drop to the lowest REV. Drops to 1700 then to 1500 when it should drop straight to 1500.

Just wanted to let you guys all know the specifics of my problem. If any knowledable tranny guys are reading, lemme know if a hanging valve in the tranny sounds right or if its the PCM or something else.