So i just bought this 1989 f150 and it has been having fuel pressure problems since i got it, i’ve replaced both fuel pumps, fuel tank selector valve, high pressure fuel pump, fuel filter and fuel pressure regulator. truck idles and drives for 10-15 mins and fuel pressure drops and turns off, sometimes it starts right back and sometimes i have to let it sit for a couple of minutes for it to start back up,

 

Two things come to mind. I would first examine your ECU for any of the three capacitors which are bulged out or leaking. Second, check to see that your fuel pumps have a good ground and are receiving battery voltage.

What are your actual fuel pressure readings at its best and what the pressure falls down to.

 

Psi was at 47 when idle, psi just starts dropping till the truck turns off, i can also hear the high pressure pump die right before the pressure drops,

 

Like other member said The ECU control's fuel pump. I would back probe the pump wire's @ the plug to confirm voltage and ground. I assume you checked the Fuel pump relay ??