Transmission ?
 

I have a 1988 Chevy caprice classic with a 4.3 7004r trans. I drove my car on a 25min. trip and it was fine. After my stay I went to go and the car wouldn't shift into 3rd. I pulled off and found the trans fluid was 3 qts low. I added fluid until it was full and notice my front pump seal is leaking severely. My question is, with that seal leaking that bad would it stop the trans from shifting into 3rd gear with having the right amount of fluid in it? Also if I am on flat ground and get the rpms up it will shift into 3rd but goes back into 2nd when I leave off the throttle.

The 3-4 clutch pack is destroyed from being run low on fluid. Damage is done keeping the level right at this point will do nothing to to get 3rd and 4th gears back. Time to replace or rebuild transmission. Sorry for not having better news. The earlier 700R4s were notorious for pushing out the front seal and dumping fluid. There were several fixes at the time to help elevate this problem. Good luck.

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thanks, that's what I figured. Just wasn't sure if I could have got luck since I wasn't having any issues until the leak started and didn't drive very far being low on fluid.