try changing the oil in the tranny... add a can of seafoam, and run it for a bit... then change it out again, add more foam, and just use it. That shit is amazing. My wife's old POS car wasn't shifting properly, tried a tranny-tune-up, with no success, then the shop said that it had to be re-built/replaced. I did this with it, and within 2 weeks it was shifting like new.

We put an additional 150,000 K on it before we finally retired it. 89 Corsica - 575,000 km. RIP