I agree that it sounds likely that you are losing fuel pressure. Have you changed the fuel filter yet? It would be good to start there. If the old filter is not plugged and the problem persists, then you should get a fuel pressure gauge hooked up and see what happens to your fuel pressure when it is acting up.
It is also possible that you have an ignition problem and that is why it would be good to check the pressure before you replace the pump.
