You can get codes with a jumper wire on a truck that old. If the MIL isnt on, there wont be any stored codes.
You need to perform a fuel pressure test. Put a gauge on it, tie it to a windshield wiper and drive it. When it acts up check the pressure, makes it easy .
If you think it could be the pump loses power take a wire and tap into the grey wire back near the tank, then hook it to a small light bulb or test light and put it in the cab where you can see it and the gauge. If the light goes out or dim and the pressure starts to drop and the truck starts to run like crap then it is electrical.Be sure to check and clean the ground wire that comes from the tank harness to the frame.It should bolt to the frame sonwhere close to the tank. It will have a bolt to the frame with a 13 mm head on it. Take it off,wire brush it, sand the frame spot that it touches, put a little grease on it to help keep it from corroding right away, and continue.
If the power stays constant but the pressure drops and the truck runs like crap, then I would suspect the pump or regulator.
If the truck runs like crap and the pressure stays good say at 13 lbs, then you have eliminated the pump as the problem.
You can do the fuel gauge thing first to see if it is fuel pressure.If it is then check the power supply to be sure it isnt the power or ground.
If it is electrical and not the pump, the issue could be corroding wiring or a bad /intermittent oil pressure switch, as the switch powers the pump after oil pressure is made by the engine.keep us posted