My fuel pump slowly looses pressure. I have replaced check valve and filter.
It pumps up to 60PSI but falls to 55 in a few min, after 10 min it is 50, 30min it is 46psi. after 20 hours it is 20psi. I disconnect the injector line from the fuel gage tee and it still drops.

 

Did you check the internal fuel line for pin holes?

 

I replaced the check valve. The high pressure line and check valve are 1 piece.