I have a 2001 Tahoe LS with 169,000+ miles. I was feeling a clunk/ ever so slight hesitation between 2-3 gear. Not all the time and not always at the same acceleration speed. I then started feeling a clunk when coming to a stop. Like second gear was not down shifting to first until I stopped. Then when I would accelerate from a stop it would feel like it was starting out in Second gear then down shift to first then it would shift normal except between 2-3 I would get that clunk or hesitation. I would also notice that it would shift into overdrive at low speeds(less than 40) if I was just slowly accelerating. Feels like it is really bogged down. I took it to a local guy and he couldn't find anything or get the trans to slip. He says "He took it apart and did a complete front to back rebuild of all the soft parts, races, seals and I assume (have to check with shop) that he replaced the shift solenoids and put in any updates that it had come out since. Now that I have it back, it down shifts just fine and has no hesitation on acceleration. But I still have that hesitation/clunk between 2-3 again not all the time. It happens mostly during slow acceleration and sometimes you can still feel it at mild to heavy acceleration. I feel that it shifts into overdrive too soon at slower acceleration. The guy at the shop told me that it's not a new transmission it's a rebuild so it won't feel like a new trans. "I don't buy it."

Can this be the rear end making the noise/ hesitation?
Are these issues caused by the computer?
Would a programmer/chip solve these issues?

Sorry this is so long just trying to give as much info as I can.
Thank you in advance for any help or advice.

Ty