2005 F-250 5.4 - P0193 - High Fuel Pressure, New FRPS and FPDM

I'm chasing a P0193 on a buddies 2005 F250 with a 5.4. Gone through the diagnosis listed in the service manual. Wiring checks out fine from the fuel rail pressure sensor back to the PCM with a multimeter. The sensor seems to be working okay, as if I manually provide power to the fuel pump, I can get my scan tool to show anywhere from 1 PSI in the rail to 77.4 PSI, depending on how long I run it for. When I have the FPDM connected, I sit right at 77.4 PSI, and the pump runs continuously. With the FPDM unplugged, I do not get any codes like a P1233 to show that is offline. I am thinking the ECU is not controlling the FPDM. I have checked the wiring between the PCM and the module, and it all ohms out okay. Not sure what the next step is. Any help would be greatly appreciated.