We are Sincerely sorry that after installing the used transmission you purchased and supplied that the speedometer is off 3 miles per hour. It must be an internal gearing problem with the unit. The drive gear on the end of the cable is the same on as what was in the old trans unit.
Thank you for bringing this to my attention. We will do our best to inform the next customer of the potential problem they may have with their unit.
Luke, owner, Luke's Automotive