You should just replace the pump regardless. Usually, most auto parts will start to show signs of wear and then sooner or later they will quit, sort of like disc brakes. Both. A failing fuel pump can just give out completely or if it's significantly worn it can work at times and not at other times. Some will fail after they heat up, it all depends on what part of the fuel pump has failed. Like the above answer suggests, just replace it. Check your relays, I just repaired a neighbors pickup that would start sometimes and then not, and just die and not start up for a while, while testing whenever it would not start the fuel pump could not be heard, I tracked it down to the eec relay, it is the first to click in the series at startup followed by the fuel pump relay, it was hard to track down since it would happen one time and not the next.