air in fuel with no leaks
I had an old sports car i brought back from the dead, would always run out of fuel at high speed. finally traced the problem to the fuel lines between the fuel pump and and the fuel.... Sucked air through the walls of the old fuel line. So I would recommend any fuel line, fitting, seal or oring in the system between the fuel, and the inlet of the pump is replaced with newer parts. There is some times a booster pump in the fuel tank, when this is the case there is also usually a short piece of hose in the fuel tank used to connect the fuel pump.
another place to look.
the fuel pump overflow.... I do not know the correct term for this, but on my fuel pump there is a check valve and if that check valve leaks, I do not have enough fuel to feed my fuel pump. Many have written this is an often overlooked part. Ask if there is such a critter on your pump. May be the source of your problems.