Rudy J,
I have a freind with an '03 GT thats doing the same thing, we have tried the IAC, cam sensor, crank sensor to no avail.
He did get a Fuel rail pressure sensor malfuntion code but that was it, he cleared it by accident and it never came back.
But its still doing the same thing, is your car also when coming to a stop staying idle at 1100 rpms then when you blip the throttle it goes back down to 600-700 rpms? He is haveing that same problem and i think it may be related, also does it backfire and kill only under cold start up or is it doing it every time you start it?
Did you try the alternator idea like the guy said on the modded mustangs forum? If so did it work?
Extra tid bit for anyone who wants to sctrach there head on this problem, since he has remote start on the car I tried this to see what it would do, cranked,car tried to start then exhaust pop with puff of smoke then dies, continued cranking for a few seconds, another exhaust pop with puff of smoke(car did not even try to start), kept cranking for a few seconds then timed out.