Do a visual inspection of the fuel lines, usually a fuel line that allows air in it also allows fuel out so check for leaks. A suction line can draw air in when the engine is running and can leak fuel out when the engine is off. Pay attention to the banjo connectors as they are frequently the cause of leaks. I gather you are running an electric pump, have you by-passed the mechanical lift pump or are you pushing fuel through it. Any component along the fuel lines can develop a leak or an obstruction. Can you start re-start the engine after it quits or do you have bleed the air out before it will re-start? Air seems to be the logical culprit but if there are no leaks and the engine re-starts without bleeding, I would suspect the fuel pump. Electrical components can fail in erratic ways; the pump could be working fine while it is cool and then quit when it heats up. I do not suggest you go out and replace the pump until you have determined it is indeed at fault, but I do suggest that you check its pumping action at the time the engine quits. I doubt your electric fuel pump is OEM equipment and their installation and configuration seems to bring additional problems and they usually have to do with air leaks. I guess more fuel lines and more connections yield more opportunities. good luck.