My 96 is having issues with slippage into 2nd and it won't shift into over drive.

I'm curious if doing a tranny flush and filter change could have any adverse effects or if adding any additives (the crap you see at autozone for slipping trans, ect...) or if it could help.

I know over drive doesn't work because my rev's are 3.5k at 70mph and when i use cruise control and try to slow down and reset the cruise the rpm shoots up and the car lunges forward.

I've heard that changing the trans fluid in cars with 100k+ miles can sometimes cause issues, this car has 144k, and i'm not very familiar with working on auto's, i've rebuilt a few standard trans but not enough to be a expert so i'll most likely be taking it somewhere to be rebuilt if that's the only option (i still plan on getting a rebuild when it's at a more convenient time...)

 

Changing the transmission fluid and filter may help if the slipping is minor, but seeing as how it is slipping AND you lost overdrive, I think its time for a rebuild.

Dont even bother with a flush or additives, they wont help your trans. The flush will probably make it worse than it already is and the additives like to foam up the fluid in the transmission which sometimes makes it worse as well.