Difference in fuel pumps?

Ok so still no vacuum test then?
The vacuum test will tell you if the arm is being stroked by the eccentric. Just cuz the eccentric is there, rotates, and looks like it has the proper up/down action, doesn't automatically mean it's compatible with your pump.
Say you bench test the pump and it pulls the spec'd 10 inches. But once it's installed, it only pulls 2 inches vacuum. Maybe 2 inches is not enough to lift the fuel out of the tank, up over the top, down the pipe and up to the check-valve. That would indicate that the eccentric is not stroking it the same as when you stroked it manually. Maybe the pump is bad. Maybe it has the wrong arm on it. Maybe the eccentric is not stroking far enough. Maybe the install was iffy. Maybe for whatever reason the pump cannot pull it up. Maybe the E-pump can. That's what the Vacuum test is designed to discover.
I mean two pumps in a row? No vacuum equals no pumping.