3406E Losing fuel prime

Had a cracked head on our 3406E, Replaced the head, installed new injector O-Rings, replaced all fuel lines to the tank, and up to the transfer pump, Replaced the check valve, replaced fuel primer pump, replaced all fuel filters.

I put air to the lines when i hooked them all up to make sure they werent leaking as i installed them.

The only way i can keep the truck running is by pressurizing the fuel tank, and cracking the first fuel filter to bleed air out of the suction line. Truck fires up right away, seems to lose prime after it sits a short period of time.

I have not checked fuel pressure, or vacuum on fuel lines as i do not have any gauges handy.

 

only have 1 tank, its not plugged. what does leaving the caps off after starting do. Injector O rings are installed correctly, I double checked as i put them back in