1994 Chevy Camaro My car won't Move until it warms up.

Ok. This ones a bute! Just bear with me here. A little history first if you don't mind. It all started a few years ago, when, while shopping at foodtown, the loud speaker came on and asked for the owner of a teal camaro to come to the desk. Of course. That was me! Apparently, my car had slipped out of park and gently rolled into the middle of the the parking lane. I brought the car to the local mechanic (mistake #1) who made the repair. Upon getting into the car, and trying to take off. It was a DOG! Could barely get out of its own way. I promptly turned the car back over to the mechanic to fix it as it wasn't like that when I brought it to him. A day or so later he called me and told me to come get it and that he found no problem. Condition still the same. I then brought it to Pep Boys who looked at it. Comparing my linkage to another camaro already there for a diff. Repair. Pep Boys told me the linkage was fine, and couldn't find a problem. Told me I needed a new Trans! I have since babied the car so as to not whine it out! The car sat for almost 2 years until I put it back on the road this past month. I noticed an improvement in its performance. After hitting the automatic starter and letting it warm up for the ten minute cycle, and then getting in it and driving, a vast improvement was noticed. It had gotten ALOT BETTER! Still not a hundred percent, but at least I was no longer pissing other drivers off when taking off from a traffic lite! Anyway.I just had the transmission fluid changed. Last week(BIG MISTAKE) Now the car needs about a half hour to warm up before it'll move again. And it isn't remotely close to how it ran just the week before. Its like it has no compression in the trans. The engine is fine. The torque converter seems to be ok. So what else could it be. My current mechanic insists that no o-rings are missing. It needs to warm up to before driving, and it is struggling. Sorry for the disertation, but I think it could be important. Please help!