Transmission

I have a1995 ford exp.4 by 4 automatic. I took it to a shop and it was put up in a diagnostic machine and it said that the speed sensor was bad, I had a trans mech. Rebuilt the trans and I still have the same problem. It changes gear when it wants to. I cant run it far due to it takes a long time if that to catch speed. I need help the diag. Mach cost 45.00 dollars to check it. I dont want to pay that again. Please advise me thanks