I've been through much of what you state.
Symptoms: Slide refused to move, jacks did moved then quit.
Repair: pulled motor, repair shop shorted the thermal limiting switch in the motor, (Mercruser J something or other, as stated above) replaced. Worked fine.
New issue:
Symptom: Jacks lower, big slide goes out without problem, but when trying to retract, the slide will run, then stop. releasing and re-engaging switch will cause the slide to begin moving again then stop. Repeat several times and eventually it will come all the way in.
Repair: Haven't completed a repair, but the a hydraulic expert suggested it's probably the toggle switch. I have a replacement switch, but am not going to try to fix it until it's broke.. (hopefully never!
) Another possibility is one of the solenoids. I did have an RV repair shop offer a 'repair'.. Replace the system using some 'adapter', total cost $5k..