Hard to diagnose in the ditch but maybe this'll help pinpoint the problem. No good just throwing parts at it.
Do the obvious and look for gas spraying from the injectors when you crank it. If you suspect fuel go to the boneyard and get some fuel line fittings etc. and rig up a gauge taped to the windsheild. Tie a light into the + going to the pump and put it where you can see it. No pressure and the lights on, relay control circuit's OK,wiring or pump. TBI pressure spec. is 12 PSI. If it is the pump, I find it easier to pull the bed off than to drop the tank. 8 bolts,tail light wiring, and 4 screws on the filler neck. Set the bed back a couple of feet. Much easier.
When it dies pull a plug wire and stick a screwdriver in it and hold it close to the mtr. Crank it and check for spark. Should a good blue spark at least a 1/2" long. Weak,red or yellow replace the coil. And like Okie said try the dist. pickup too.
It's also possible the Auto Shut Down relay's coming unlatched,in which case you'll have neither spark or fuel.