If you get no pulse, it may be the computer is not turning on. But. If the fuel pump runs for 3-5 seconds when you first turn the key to ON(listen closely for the sound), then the computer is at least 'awake'.
It may be old enough to need a couple capacitors on the computer board replaced. If they rupture(electrolyte can due to age/heat/etc), they won't work and the computer will be confused to say the least.
If the pump does not run, check the rollover switch near the top edge of the passenger side floormat/carpet. Red button will reset. Should have voltage going to pump at key ON for a few seconds... use a test light.
The fuel pump relay is on the inner fender, passenger side, under the black plastic cover. Remove the center of the push-pin retainer, and pull the retainer out, slide the cover off, relay mounted on the side of the innder fender, contacts hanging down. It should click and provide power to fuel pump at key ON.
The distributor has a electronic box mounted, the TFI Thick Film Ignition that sends a signal to the computer that the engine is cranking... must get the signal to turn on the injectors. You can replace w/o removing the distributor, you will need a thin-wall socket of some weird size OR the tool sold at auto parts stores $3-5?. TFI's are not real expensive. The coil should have 12V when you turn the key to ON. The TFI will provide the ground to allow current flow, and energize the coil. When the computer signals, or if a manual, the distributor rotates while being push-started, the ground will go away, and the coil produce a spark. If no 12v check wires & ignition switch.
Check the belt timing by setting crankshaft to TDC, remove the plastic plug on the belt cover behind the upper radiator hose. Look at the edge of the cam sprocket for a triangle. It should line up with the pointer at TDC, or rotate crankshaft a turn, and check again. If not, valve timing will be off. Belts can loose a few teeth and still sort of work, but be out of time.
Check the fusible links on the battery side of the starter relay. They provide power to all the stuff in the truck. If the ring connectors get loose, that particular circuit won't get fed juice as needed. Check that they are all tight. You have to 'fan' them out to allow for them to ALL get seated tightly.
tom