I have a 1998 with the 4.0
Was having starting issues and bogging under load. Replaced the fuel filter. Truck seemed to run fine. Then it was finicky on starting a day later. Replaced the fuel pump relays. Just swapped out all 4 VIKKSAER 5 Pins 12V Relays F57B14B192AA
It was running fine. Brought it home. Next day turned over but seems fuel starved. Inertia switch was not tripped. No fuses blown. My search says it could be the fuel pressure regulator or the pump.
I've been reading about the fuel pressure regulator but youtube vids have conflicting locations of regulator location and where the fuel rail port is for the gauge to hook up. I'm hoping to fix this without having to lift the bed and do the pump.

 

Fuel pressure regulator is in the tank. You will have to drop the tank or raise the bed to fix it. Your truck has a return-less fuel system and you should have about 65 psi at the fuel rail for this truck. Schrader valve is on the fuel rail. Looks just like a bicycle valve. Mine has a blue valve stem cover. You need to check and see how much fuel pressure you have first. There is also a fuel damper on the fuel that a lot of folks mistake for a regulator. It is a sealed rubber diaphragm and it absorbs fuel pressure pulses from injectors opening and closing

That damper has a vacuum line plugged in the bottom of it. Remove the line and see if you can smell gas in that line or if it has gas in it, if so, a new damper is in order. That vacuum line is there to suck any raw fuel into the intake manifold and keep it from getting onto a hot engine manifold.

Good luck

 

I swapped out the entire fuel pump assembly with a new pressure regulator. Still not working. Giong to swap the ECM next

 

What brand of fuel pump assembly did you buy? Just because it's new is no guarantee that you got a good one.

Have you checked your fuel pressure? If not, you really need to check it. Like i said earlier, you need 65 psi at the rail for the truck to run properly.

The truck also needs to be able to hold that pressure while running, plus or minus 5-6 psi. If the pressure is bleeding off while running you will get that engine bogging down.

Throwing parts at a problem gets rather expensive really quick

 

UPDATE
After much research and testing it turns out the new pump is fine. It was the crack positioning sensor that had failed. Truck is running again.