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[Gofasterdammit]

Since they are all on the same bank, replace the fuel check valve for that head. The check valve is the banjo bolt that connects the fuel line to the head. After that make sure you have atleast 48 psi under WOT at the secondary fuel filter test port. You can try installing the updated fuel pressure regulator, it has a longer spring and usually jacks up the pressure a few psi. Your sig says you have a F-450, does it have the aft axle tank? If it does I would make sure all of the breather tubes are installed and pull your primary fuel filter and check for fuel tank delamination. Aft axle tanks are prone to get water in tank.