Find as many grounding wires as you can, and make sure all the spots where they ground are clean and tight!

Make sure you are getting enough fuel pressure to the rail. (36 to 40 lb.) Pump may be weak, or even, more possibly the fuel filter is restricted and causing low pressure. It sounds more like the filter is the trouble. It's clogging as you drive, and after it sits a while the dirt settles,and then it will run again for a short time.

Main realy could be the problem also, but good luck replacing it. The easiest way is to remove the screws along the top dash rail, unclip the black face plate, and then the speedometer/tach unit. You can get to the bolt then, possibly!

But if all that stuff is OK, then check the injector relay!!! It's at the left rear corner of the engine compartment. Good luck!