05 silverado fuel pressure

Snow plow truck, 05 silverado 3500 dually dump truck, has 2 fuel tanks
Primary and Secondary (2 different pumps). To my knowledge the
secondary, pumps fuel into the primary. Used for snow plowing in winter
only. Fall of 2013 I changed both pumps with OEM acdelco pumps. Worked
fine for winter of 2013, about 50 days into the 2014 season it started taking
3 to 5 seconds of crank to start to having to cycle the key 4 to 5 times to
get started. I figured it had a bad check valve so I replaced it with same
pump made by delphi in Dec 2014. It started doing the same exact thing. I
put fuel pressure gauge on it and when key is on it pumped up to 55 psi.
After 3 seconds pump stops and pressure drops to 0 immediately. I took
the first acdelco pump and put a check valve on the pump in the line that
runs from top head to bottom where pump is. Put it in and it held pressure
and started. Next morning pressure gauge was 0 but truck started right up.
4 days later pressure was 0, when starting it I had to cycle key 5 times to
start. Now these primary pumps have the pressure regulator right in the
pump housing in tank (Called Returnless Fuel Injection Systems) no lie. It
has 2 electrical connecters on the fuel pump head. I'm guessing one tells
the ECM or something fuel pump pressure. Pump P/N is ACDELCO
MU1419 or Delphi FG0353. I'm about to order another fuel pump. Is it
possible I got 2 bad pumps and a bad check valve or is there something
else? I don't know the fuel line schematic or electrical schematic. No leaks,
does not use excessive fuel.