Hello!I am Forrest from the ForrestMelissa post above.My truck is a 2003 gmc sierra 1500 4x4 5.3 liter. I have replaced the fuel pump, fuel filter , mass air flow sensor, air filter, throttle position sensor, map sensor, fuel pressure regulator, spark plugs, wires, all 8 coil packs, evap canister purge valve, crankshaft position sensor, and the pcm. The truck starts up first try when it is completely cold and it will idle fine until it reaches normal operating temp and the it sputters and stalls out and won't start up again until it is completely cold again. I am at a complete loss on this. I am no mechanic by any means, but I have had to learn as i go because I cant afford to put in a shop and I don't necessarily trust most shops anyway. If anybody has any ideas I would greatly appreciate some help. My truck has been down for 2 months now. I have had to borrow a vehicle for work. Any help would make a difference. Thanks! Oh, Ialso replaced all 4 O2 sensors and the fuel pump relay.