O.K. If they are all doing it, then I would suspect the solinoid valve isn't holding the pressure and it's losing the pressure to hold the slides in. (not leaking fluid externally, but internally)
The solinoid will have a thumb valve on it to bypass it manually. It should be near the pump. IIRC it should be turned counter clock-wise. I can check tomorrow for sure or some one else can chime in.
Also check here if you have a Lippert unit.