I just bought a 90 F-250 with a 5.8L engine and a E4OD auto tranny. The tranny has just been rebuilt and installed in the truck before I picked it up, and on the drive back, the speedometer seemed a little off - in fact I covered a measured mile in 60 seconds with the speedometer pegged at 70MPH - so at that point it was off by 10 MPH.
Since the speedometer is not electronic on this vehicle, and is obviously mechanical, any suggestions on how to get the speedometer to get more in synch with the actual speed?