The slide motor wouldn't turn on my 2004 Rockwood even though there was power at the motor. It turns out the brake was defective. In my case, the brake was attached to the end of the motor opposite the end with the gearbox. The brake grabs the shaft when there is no voltage to the motor. When the motor gets voltage to turn, the brake also gets 12V so it can disengage. It was not disengaging, so the motor couldn't turn. I removed the brake assembly off the motor and the slide worked fine. The brake assembly had its own manufacturer and model number, so I called the manufacturer of the brake and they sent me another one.
I don't know if your setup is the same (I have a rack-and pinion drive for the slideout), but you might want to check the brake if you have one.
Steve