Did you replace the fuel strainer (the “sock”) on the fuel pump? Does the fuel pump run? A dirty strainer could be stopping fuel flow.
Are you reading voltage within two seconds of the ignition switch being turned to RUN? Isn’t voltage supposed to be present ONLY then (for two seconds) or during cranking of the engine?
Power is supplied to the fuel pump, when the engine is running and there is oil pressure, by the oil pressure switch. If oil pressure is lost, and the engine is running, The oil pressure switch will open and cut power to the fuel pump.
The fuel pump has to have a ground. Check any ground wire, or strap, connection on the gas tank and attached to the body. Loosen and retighten any grounding screws.