i have a 1989 dodge truck, it will start and run but when it starts to warm up the idle will start to drop off and then die. I have replaced the throttle position sensor,mar sensor, injectors, 02 sensor,fuel regulator, and new plugs, can it be electric if you can help thankyou

 

I would start by hooking up a fuel pressure gauge To see what happens when it quits. then check for spark when it quits... Does it have an idle speed sensor at the back of the throttle

 

I have a 1989 W-150 as well and ran into this exact issue. if you turn it off does it start right back up and run for a few minutes before it quits again? If so then I agree with TVLynn, this sounds like your fuel pump is starting to go. How does it idle?