Looking at this diagram
http://mmeierle.com/MPI24LCircuit-1.jpeg

you are getting power from the engine control relay, wire 2-BL (black and blue) i would start checking that wire.
you may also want to unplug the ecu a couple of times to clean up any dirty connections
Good time to check any fuel filters you have


I also see you mentioned you thought it might be the fuel pressure regulator. Once the pump is working, check to see that fuel is getting to the fuel rail. If it is and the truck still doesnt start, Pull the return hose from the Fuel Pressure Regulator and see if its wet with fuel after cranking the engine. If its dry, your Fuel Pressure Regulator could be faulty.