Hi ted that is correct the truck will rev up with brake on when directon selected,it is a difficult fault for you to diagnose without laptop/analizer.If you swopped the plugs over on the solenoids and rvs worked then ths would suggest the solenoids are ok.I am assuming you have a twin pedal truck rather than single pedal with direction switch,my next step would be to change the drive pot under the pedals this just unbolts and refit new one with locating arm in slot and tighten up,you will not need laptop to do this and no set up is required.The drive solenoids are controlled by the Hyd control module(silverbox)under the air filter assy,and this would appear to be seeing a fault and stopping the truck from driving,most other components are common to both directions so drive in fwd would also be stopped.