Dodge Repair Questions? Ask a Mechanic for Answers ASAP
Sounds like the lift/transfer pump is not pulling enough fuel out of the tank. Regardless of engine RPM, the transfer pump has to provide more fuel than the injection pump requires. Once that excess fuel reaches 22 psi, the overflow valve opens and allows that excess fuel to return to the tank.
To test the system, you can either use a pressure gauge attached to the overflow valve fitting (see attached graphic), or can you temporarily rig a hose and container to verify fuel return. If tests show no fuel return, your best bet would be to install an aftermarket electric lift/transfer pump. Click here to see an example - if you're handy and have the time, the cheaper option would be to use a chassis-mounted gas fuel pump.