It seems to me that the factory never put out a system that didn't include residual valves, no matter where the MC was. The theory that it is OK with no residual valves if the MC is above the wheel cylinders, doesn't make any sense. If that explanation was correct, the truck couldn't be parked on a steep hill if it caused the MC to be below a wheel cylinder. Those valves are there to retain a positive pressure in the system and prevent air infiltration.
