Try this...Change the transmission
1. filter
2. fluid - make sure you check the fluid correctly, enging semi-warm, running, on level ground.
This should work. If it doesn't then check for other possible problems ie. modulator, etc.
If you can't find anything, then you may have to bite the bullet and get yours rebuilt or replaced.
I did all of the above and it bought me some time, but eventually the transmissin had to be rebuilt. I paid $1800 to get mine rebuilt with OEM parts. This price included removal and replacement.
You could go to the stealers to get a rebuilt one, but they'll want your old one and a $3000 deposit (Don't quote me on this amount, I can't remember the exact amount). But be careful becaue if the stealers determine that your old tranny can't be rebuilt to their specs, kiss your deposit good bye.
I had mine rebuilt because the mechanic I go to only uses OEM parts. Please don't go cheap on your transmission and use aftermarket parts, especially on the transmission....that's only asking for more problems in the NEAR future.
Fixing the transmission cost a lot of money, but I consider it a better deal than having a payment every month. My car is an 86 and everyone thinks it's a 95.
Good luck.
jrmd01@yahoo.com