I'm having problems with my 94 honda civic, everything was working fine before but then the radiator broke, we fixed the radiator got new head gasket etc. So now I drive and the transmission doesn't shift to 4. It goes to 3 but before it's going to shift to 4th it stays neutral. The car also doesn't reverse. Also, white smoke comes out of the muffler, sometimes a lot sometimes a bit. How can I fix this problem?

Also, the car doesn't reheat. We tried changing the transmission fluid, the first time we emptied it, 1 gallion of transmission fluid poured out. We refilled it, for a while it was able to go on reverse and 4th, but after a while when the engine like gets heated (car doesn't overheat) it doesn't go to 4th it stays neutral.

Today we were told to buy the tranmission fluid from the dealer itself, empty it out completely, turn on the car, and after a while fill the car with transmission fluid again. Only now this time it won't even go to reverse and 4th, not even sometimes, that sometimes is gone lol. We're back to where we started in the first place, any ideas how to fix this? :S

White smoke is antifreeze being burned in combustion. The head is probably warped and leaking antifreeze. Transmission likely needs rebuilding.

Does this mean we have to buy a brand new transmission? :S

Likely a rebuilt. Check around for the best warranty and price.