Had the same problem. Mine is electric and one of the slide motors was bad and therefore the one on the opposite side was doing all the work. Check the motor on the side that sticks out to make sure it is working.
Vera & Ken
1998 Holiday Rambler Imperial, RR8S Chassis
Cummins 6C8.3 mechanical engine, 325HP, 3060 Allison
Towing 2014 Ford Explorer