93 Lumina APV transmission trouble

Hopefully someone can give me a little insight. My Lumina was sounding a little funny last week on the way home. I realized that it was stuck in 2nd and whining. Could smell a little burning sometimes too. I checked the tranny fluid and it was full, but added some slick50 automatic transmission treatment. Still it wasn't going out of 2nd :disappoin , so I figured I'd call and make an appointment to get the fluid changed and bands adjusted. The tranny shop asked what problems I had so instead of changing my fluid(like I wanted done), they said to drop the van off and they would do a "free" diagnostic check. Sounded good to me, then they called 2 hours later and said that I had 1st and 2nd only and some burnt fluid. This told me nothing but what I had already told them. :banghead: So they suggested to get a computer scan "This will give us an indication of what is going on" So I agreed and they called me an hour later to tell me that I had multiple codes. They said that it says I have a shift problem. Ok. I already told them that, and now it cost me $65 for them to tell me that I have a shift problem. :screwy: Now they say, "Now we are going to have to take the tranny apart to find out what is wrong" It will be $1200 to take it apart and then I will have to pay for parts and labor to fix it. I tell them that I can't afford that right now and I will be over to pick up the van. They still try to get me to leave it there--'you can finance it, or borrow money from family' I was really mad!
Does anyone have any idea what could be wrong. The engine runs great and it shifts from 1st to 2nd nicely but then that's it. I haven't driven over 35-40 because it won't shift. I haven't smelled anymore burning. Please help with any ideas.

Well, I have a similar problem with my '93 APV. If you have the 3.1l engine, the tranny gets it's shifts in part by the cable going to the throttle body. I disconnected it and gave a few good pulls. That solved the problem the first time through. Now it is doing it again- I haven't looked at it yet.
Mine shifts really well, but hangs in 2nd when it's cold. My guess is that it is either that cable again or the bands/modulator needs to be adjusted.