When the car shuts off, does it crank OK? In other words, does it act like the battery is dead, or does the engine sound like it is turning over OK, but wont seem to run? You mention that the fuel pump and the starter have been replaced, I assume by a repair garage, but they have entirely different symptoms when they fail so thats somewhat confusing. Different problems, with different possible causes; I need a little more detail as to what exactly happens when the problem occurs to be able to offer any kind of meaningful help on this one...