'88 F350 460 Hard Start

Have a 460 F.I. which suddenly will not start without the introduction of ether to the intake. Fuel pressure gauge test reveals 40psi on the fuel manifold after ignition switch to on position and also after long periods of no usage telling me the fuel pressure regulator is O.K. Replaced fuel pressure regulator, main electrical fuel pump and fuel filter twice. Engine will fire intially, then stall as if out of gas and will not refire again without ether......but with only a very small amount required. New distributor cap, rotor, plugs, distributor module, stator, engine temperature sensor, throttle position sensor. Need HELP :

Have you tried holding the gas pedal down when you start it. THis happened to me when my IAC died.