If it is a schwintek slide the first thing to try is:
Retract the slide, until you hear the motors stop turning. Keep holding the switch to retract for about 3 seconds, then release.
Extend the slide, but only a couple of inches. Do not go all the way out.
Repeat the above steps 3 or 4 times. See if that corrects your issue. Again, for schwintek slides, I don't know if it works for other types.