Did your fuel pump sound pretty loud, almost like priming while driving? Mine is not having that bad of a drop but slowly drops and gets to about 20 psi in a few seconds after the initial prime when you turn your key to the position before cranking the engine. I replaced my fuel pump and my new one is constantly loud and almost priming while I drive. During engine run, it holds pressure nicely so I'm sure I have a leak maybe didn't get the circular plate above the fuel pump not 100 seated well. But let me know if yours is making that same noise.

 

The fuel pump will run while the engine is running , what brand pump did you get?

 

Got a Delphi. But ya the fact it looses pressure instantly after primed, that's odd. Let me know if I should do a new thread so I don't take over this one.

 

I’ve moved it to it’s own thread

 

Ok I made a video to show exactly what is going on. It's holding pressure better after I dropped the tank again today and reinstalled everything. But it's still making an almost priming sound when the engine is running which it shouldn't be that loud. When I turn off the engine it drops to about 40 psi and stays there for a little while and slowly drops. Not sure if the two issues are connected or not. I did take a video of the pump when primed with the pressure.
https://photos.app.goo.gl/pM4eUwheqexN2hFXA