Jerry,
a full model number and serial number would be more helpful.
but like garland said, most lifts "after" a certain year they started putting encoder bearings in the motors, these generally are in the newer AC drive control systems. Depending on your model and serial your machine may or may not have this. Also generally if your display on the dash (if you have one) would be displaying some sort of error code for this when the problem occurs unless it is hardset, then it would show it full time.
But as i mentioned at first, knowing your model and serial would tell us what system you have in the lift. THEN we can go from there.