I have an 08 chevy Silverado 5.3 liter flex fuel with 70,000 miles. I have been having nothing, but problems with it. It has been starting and running rough for a little while and today it just starts and shuts off. I have been trying to figure out rough idle for a while with no luck. I replaced mass airflow sensor, crank position sensor, cleaned throttle body, have good fuel pressure at rail, replaced spark plugs and wires (truck was running rough before I replaced plugs and wires), no check engine light on, and I have smoke tested truck. I now notice that the fuel pump is not priming everytime I put key in on position. Even if it does prime it will only start and stall right out. While starting i have pressure tester on fuel rail and pressure stays right around 55psi. I also tried swapping relays for fuel pump and checked fuses and found nothing. It would be great if I could get some help here as I have been pulling my hair out trying to figure this out. Any help would be greatly appreciated!!!

 

55psi is kinda low, should be 65, if you don't hear pump at key start I'd be very suspicious of fuel pump..