chk engine lt on, and no shifting ability

Please help!

I have a 2000 Acura Integra LS 2 Door AUTOMATIC Trans. with about 101,000 miles on it.

I recently had a tune up about a month ago, a transmission fluid flush and exchange, and I have had an oil change. I also, had a smog check done about 3 months ago, and it passed with no problem.

This is the second time this has happened to me. While driving at about 20 mph, my check engine light comes on, and my car will downshift itself and then after coming to a stop, and then accelerating again, it will not shift from 1st to 2nd. (This is an automatic trans)

Also, when driving at about 60 mph on the freeway, and when I am coasting at about 2200 RPM, my car seems to be hesitating and it's as if it is adjusting itself... Almost like a fuel injection issue.

I have taken it to Acura and they advised me I needed an entirely new transmission at $3900.00. Of course I freaked out and took it to a transmission specialist. He hooked it up and determined that everything was fine, no leaks, solenoids were fine, etc. I also took it back to where I had the tune-up, transmission fluid exchng place, and they said I needed a TP Sensor (Throttle Position Sensor)

I am so lost and frustrated with this.

Any IDEAS on what could be happening would be greatly appreciated???

Have any of the places pulled the check engine code? Seems strange that 2 different places would tell you 2 different things unless only 1 of them pulled the code. Especially Acura telling you that it was the tranny and the other place testing it and it being fine. Maybe try taking it to an some place like Pep Boys and having them pull the code, I believe some people said they do it for free.

but why would the check engine light come on for a tranny problem?