So I vaguely remember something about something in the tank being the issue as well. It was a few years ago however.

 

Finally some success. Hooked up tank from an 06 wreck. Cleaned up the tank but did not mess with the tank cover/pump/etc. Jumped relay, pressure was over 65. So proceeded to installed the tank and all is well.

So the issue had to be one of the two thoughts above. Tank cover or maybe some sorta check valve/ball/float in the "secondary" filter hat output on the swirl pot. If the second, then there maybe are cases out there where suspected fuel pump failures are not intact the pump itself but the swirl pot in some way. And since replacing the pump itself is not normal practice, folks replace the entire assembly and all is well. No matter since a whole new assembly means all new filters. So no downside really.

In the pic, that metal retainer slides out and then there are some parts that can be removed. This is the area I suspect thing could go bad. The upper filter donut actually has two outputs. One to the regulator/tank output. But then strangely an output that goes downward past the pump to this weird part on the bottom of the housing.

 

Found this tid-bit in the manual:
A one way valve is located in the base of the swirl pot. The valve allows fuel from the tank to enter the swirl pot, but prevents it from escaping.

I will be taking the base apart on mine if I have time and inspect for this valve.

 

I have recently learned there is a check ball in the fuel filter of a Porsche Cayenne as well. Crazy way to do a design