The street side (under bed) slide is electric, but the curb side is hydraulic. The solenoid manifold for our '06 is up front underneath on the frame near the entry step. You might want to first check that the release nut on each solenoid is tight; there is a 1/4" nut driver for that purpose on one end of the reservoir cap. HWH recommends replacing both the in and out solenoids for a given slide, if you replace either. You may have to consult them or their website to help determine which solenoid set is which, and how to properly replace them. Just listening, with the head end of a large screwdriver to your ear and the drive end to each solenoid, while someone else operates the slide, may help figure out which solenoid does what for which slide.
-Joel