Honda Repair: 91 Honda Civic LX, auto transmission, 91 honda civic

Question
My Civic Shifts into all 4 gears just fine until the car has been driven for about 10 min or more. Then it stops shifting into 4th & if driven longer it eventually stops shifting into 3rd. Will replacing the tcm fix this? Or, if not, what should I do?

Answer
Bobby, tcm? Transmission control module? First off no such thing. You didnt describe whether you had a Auto or Manual transmission. Whichever i will assume this is an Auto. Manual follow the same guidelines too. Check the level of the fluid in the transmission. And correct as necessary. Perhaps flush the transmission system would be ideal but, cost around $50. Auto transmission use Honda ATF. Manual Transmission use appropriate specified oil (synthetic).