Difference in fuel pumps?

Agreed! I recently got two bad pumps from AutoZone, two different brands.
Got one from O'reillys that worked. But if you bench tested it you've got some other problem.
I put a screwdriver in the hole and turned the engine over with a remote switch, I could tell the eccentric was moving up and down like it should. Suggest you try this.
Cam bolts have been known to loosen, why I always use lock-tight on 'em.
I'm sure you'll find it, before I knew the pump(s) were bad I put more gas in the tank, and blew compressed air through the lines, realized I should have tested the pump first!
Let us know what you find.