Generally speaking, electric fuel pumps rely on the fuel to keep them cool and lubricated. Any air entering them can cause the vanes to crack or shatter. I would start with a complete test of the pump, meaning flow rate and pressure, not just a pressure test. If you know that you are loosing pressure, then I would start with the pump. I'm uncertain if this pump has a separate pressure regulator, but if you are going that far, you might as well replace the pump... Just through another $1000 st it...
