Don't know if you're still fighting this, but check to see if the fuel
pressure regulator is draining the fuel pressure off back into the
tank. To do this, you'll need a pair of needle nose vise grips, and
if you can obtain a fuel pressure gauge that'll help.
With a helper inside the car while the engine is running, have the
vise grips ready to pinch the fuel return hose clamped onto the fuel
pressure regulator. Have your assistant turn off the engine. As he
does so, clamp the return hose shut. Allow the car to sit the
requisite amount of time for the condition to occur and attempt to
restart it. Allow the engine to run only very briefly with the vise
grips installed, as the fuel pressure will be very high due to the
blockage of the return hose. If the condition does not occur, the
problem is with the fuel pressure regulator.
If you have a fuel pressure gauge installed, you can simply monitor
the fuel pressure. If it drops when the return line is pinched but
not when it isn't, the problem is in the fuel pressure regulator.