Since your slide out unit is hydraulic type, I would do the following to trouble shoot the unit.
I. Install gages hydraulic type pressure gages, at the lines form the pump to the cylinder or motor.
2. Use these to see what the hydraulic pressure is when actuating the pump. See if enough hydraulic pressure is building up from the pump to move the cylinders and or motor. You maybe leaking fluid internally in either the pump, cylinder or motor, bad seals. This would then prevent enough pressure in these components to retract or extend the slide fully.
3. If the pressure is above 1,500 PSI or 2,000 PSI, then the slide is stuck and will need to be adjusted. I am not sure exactly what pressure it will take to move your slide it might be even higher than 2,000 PSI (this should be in the O&M guide).
Check out this site for information on slides and adjustment.