problem on highway and shifting

I have a 95 camro 5.7 and i've been haveing problems at first i thought it was the transmission after haveing it rebuilt and back into shops there's nothing wrong they tell me.Does happen in drive only while driveing with the car in overdrive sometimes while shifting it will hesitate before it goes. Then on the highway while crusing at a constant speed the rms will keep droping and then going back up causeing like a jerking motion if i were to let off the gas or hit it hard it will stop. Is this normal? It's anoying and i have loudmouth exhaust so it really noticeable in the sound now when it happens. I've tried replaceing the TPS but didn't make any diffrence at all. Please help!

Does it only do this at high speeds or what? I'm thinking it could possibly be a ignition problem...

i does tend to do it alot around 70 at about 2400 rms and it will keep droping to about 2000 rms and back up again it doesn't do it at low speeds just the shifting problem were it will drop and kinda hestate then go. Never does it when you get on the gas or out of over drive that's why i tended to think it was the tranny at first.

How does it do wide open throttle?

It's fine only happens at lower rpms