I agree with John Wayne, the motor's brake ( under rubber boot at the end of the slide's motor)is not working correctly. Pull the rubber boot (cover) off and have a close look at the brake mechanism. The brake mechanism may be sticking or seized, it may only need some WD40 to loosen it up.
Ellen & Greg
08 National Dolphin DL-35Ci, RoadMaster Rear Sway Bar, Rear Trac Bar, Koni Shocks Front,
Workhorse W22, Kelderman Air Ride, Towing 2016 Smart Car