95 F350 trans problems

a friend of mine has a 95 ford F350 that he pulls his 28 foot race car trailer with. he has had to rebuild the trans 2 times and the person who is rebuilding it says the computer wont clear the codes and cant fix it until he clears that the problem was that it would shift hard and then would choke the moter down and when you put it in reverse it would want to go 50 MPH in reverse. he said it did not slip or chatter the only thing it did was the check engine lite came on and went off several times until eventualy it stayed on. it is a E4oD any help would be great!!!