My Lippert slide has 2 motors that can get out of sync and the way to synchronize them is to hold the slide switch in until both sides of the slide are fully closed. These 2 motors are at the top of vertical drive screws mounted on the stationary wall on each side of the slide. The vertical drive screws connect to aluminum rails with teeth on each side of the slideout. It would be easy to count the teeth showing on each side. There is also a controller PC board that flashes codes when queried. Mine is nearly unreachable behind kitchen drawers which must be removed to access it. In the 10 years I've had this trailer it has never gotten out of sync but I always hold the slide switch for a couple of seconds after the slide is all the way closed.
Perhaps your Lance is totally different