Just bought it, its got some fixable issues, 5.0 5speed. Pulled it in the garage to put new shocks on it and it would not start 2 hours later, just cranked and cranked. Finally it started and i pulled it out into the driveway and left it running. About 25 seconds later it just stopped running. i did not test anything just went and got a new fuel pump relay as that was the cheapest. Now the truck always starts. My question is could a bad fuel pump relay cause it to sometimes start and would a bad fuel pump relay cause it to just stop running like it did?

Im new here and so far its a very informative site!

 

Sure - if the fuel pump stops pumping it doesn't run........

I would advise you to change the fuel filter.