Ok.. Lets start simple...
Do you have stock fuel pick up unit? Is the screen intact? Is the screen plugged up?
Do you have debris in the fuel lines? (Rotten rubber, trash, etc)
What kind of pumps do you have? How old are they? (miles / Time)
I would start over again and inspect from start to finish. I would start at the tank and inspect the fuel pick up unit and the inside of the tank. (Yes this requires lifting the bed) After you sure the pick up and the contents of the tank are fine move foreward up the line. Make sure you don't have rubber flaking off and jamming up you LP pumps. I would disconnect all line and blow them out. (Yes. Now you got to reprime the system.) But you'll know the lines and the pumps at this point are clean. If you haven't change your filter do it now and drain the filter housing in to a container and inspect the fuel for debris, water, gelling, etc...
As fore the pressure there is a OVERFLOW VALVE on the VP44 pump. It can be tested with a blow gun. Sometimes the check valve will hang open and dump all the pressure back to the tank.
Something you wrote maybe you should follow your own advise...
Fuel System Troubleshooting Guide
You taugh me alot by writing that article...:thumbsup
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Michael Nelson - 2002 Dodge Cummins
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