We have a 2WD short bed, dual tanks. Replaced front tank, both pumps and filter on Easter weekend 2014 and probably have less than 1000 miles since then. We have intermittent issues where the truck refuses to start. It seemed worse when tanks were less than 1/2 full. Tried relieving vacuum by opening the filler cap. I checked fuel pressure over this past weekend. It was at 54 psi with key on, engine off. While cranking it dropped to around 40 psi. I figure either a blockage in the line somewhere between the filter and the fuel rail, or a voltage drop. We tried blowing air back through the supply line after disconnecting from the filter. Very little came out. Apparently most of the air followed the return line back to the tank. Is there a check valve in the line between the filter and the fuel rail? I don't see anything that looks like one. Added more gas to the front tank and it is now almost full, but still won't start.
Once it starts, it is silky smooth, good power, no issues unless it vapor locks on a hot day. We have also replaced just about every sensor under the hood, verified the IAC works, replaced fuel pressure regulator... I'm really not convinced that the lines are blocked, but something is causing the pressure drop.

If I was to replace the stainless steel fuel lines, where would I find them? LMC Truck doesn't show those parts for EFI systems, and I have not used other suppliers.

 

in '90 with dual tanks, do you have another external pump and that messy tank selector valve thingie? Or is it a single high pressure pump in each tank with simple-ish lines heading straight to the engine?

I pulled my lines from a newer 93-96 pu and it had the high pressure fuel pumps in each tank. I assumed that there is a check valve somewhere to handle the switchover between tanks as all there was was a simple T for plumbing the front tank.

The drop in fuel pressure with engine running might be normal with the engine consuming the fuel and the regulator doing it's thing (once vacuum is applied to it).

Vapor lock would be the only thing I'd worry about if it seems to run fine but cycling the key on and off should allow the fuel pump to push air out back into the tanks return line.

 

It has high pressure pumps in the tanks. I think there is a tank selector valve, too. There is a check valve on each fuel pump where the supply line connects to the pump. It slips on the fuel pump tube with the same snap connect as the fuel line, then the fuel line to the check valve. I didn't know what they were and almost left it on the old pump when we replaced them because it was difficult to get the disconnect tool in there with the pipe bend and all. I'm glad I did the right thing, otherwise there would be no fuel going to the engine.