Several years ago I had the same trouble you're having,.....slide would start to move then motor/pump would stall out. From info obtained from one of the techs here, I installed a bypass switch on the dash which......as good as I remember, grounds the motor/pump solenoid. This in turn bypasses all the safety switches in the system.
Whenever I extend or retract the slide, I have to hold the momentary bypass switch, or the slide will not work. Since I installed that switch, the slide and jacks have never fail to operate correctly. If you decide to check out this route,.....and need more info on it, email me and I will check it out as to how I connected it.