Sounds like the hydraulic cylinder is bypassing and letting the slide room "creep" out. There should be a little valve on the side of the hydraulic cylinder; that is called the anti-creep valve. You can also try bleeding the air from the system here is how to do so below.
-Make sure the pump reservoir is filled with hydraulic fluid. There is a fill line on the reservoir.
- Using either the manual buttons or the All Retract button on the Control Panel, fully retract all of the jacks.
-Re-check the fluid level (add as necessary.)
-Using the manual buttons on the Control Panel, fully extend all jacks to their maximum extension. This will require alternating between the front two jacks and the rear two jacks – the cross frame twist limiter in the Control Panel will not allow you to fully extend one jack at a time.
-Keep the jacks extended for at least 15 minutes.
- Again, fully retract the jacks.
-Re-check the fluid level (add as necessary).