We just had one slide that would not extend. In the basement there was manufacturing trash that worked its way into the rack preventing it from moving. The pinion gear lost 4 teeth trying to move the rack.
This is probably not your problem since all 3 slides don't move. But wanted the group to make a mental note of my problem in case of future slide problems.
2013 Flagstaff 8528IKWS, 2006 F-350 6.0L