With dragging brakes, the engine would rev up and 'try' to move the RV, but not move it.
His problem is it will only idle while in gear. It will go to a higher RPM while not in gear.
All temps look normal and no engine codes.
I guess you could open the engine cover, and look for the throttle. Can you move it safely while the cover is open and engine on? Remember the turbo will be very warm, and close by. If you can see the engine throttle moving while in neutral, then have someone driving it, while you try to move the throttle while it is in gear. This might not work at all on a new electronic controlled engine, but should work on one older than 2007.
Good luck,
Fred.
