Slytown kountryboy

I have a 96 Tahoe with the 5.7 vortec...I was sitting at a red light and it shuddered out like it was out of fuel but I had 3/4 of a tank since then I have replaced the fuel pump twice along with fuel filter thinking first was defective have also replaced all fuel relays and fuses,fuel regulator, complete new spider injection assembly, air flow sensor, throttle position sensor, idle control sensor, crank sensor... fuel pump is working and getting plenty of fuel and fuel pressure to my fuel rail but still won't fire off and if it does its only for a second or two. Please any suggestions or opinions are welcome and considered Thank You