Randy,
Not trying to be a smart a$$ in any way, but back in post #7 you mentioned that you snagged the fuel supply & return setup from the Mustang and adapted it to the truck. You didn't by chance reverse the connections, getting your "supply" piped to the back side of the fuel rails where it would be trying to backfeed past the pressure regulator, which acts as a check valve? I know it's a stretch, but there's something basic wrong here. Maybe unhook both the supply and return from the fuel rails, turn the key "ON" and see if you get flow from either line?