SargeSlaughter

2004 Sierra, hard to start after its been sitting for more than an hour or two. Fuel pressure drops to about 40 psi, cranks but no start. Second key off key on engine starts. Cant hear the pump prime on the first shot so I'm thinking pump isn't priming when key is turned on. Pump is brand new, everything else runs fine when it's running. Any idea what could cause this?

Misfire counter shows its all over. Sometimes it doesn't start and takes 2 or 3 tries to get it going. Also I noticed the Delphi pump I pump in it has a working pressure of 54psi and the spec on these trucks is 55 to 62. Could that be a possible culprit? I checked pressure while the line was primed and am only get about 50psi. Maybe a bad pump?

And just changed the cam position sensor with no luck

No fuel pressure regulator on this one

Does anyone have any advice where to start looking for a P0300? Truck has LM7 with 188k on the clock. Runs fine until it starts to warm up or going up a grade and starts missing and spitting. Things I've replaced over the last year, throttle body, maf, map, cats and all o2 sensors, plugs and wires. Replaced coils 2 years ago. Fuel pump was just replaced with a delphi, check engine light would go on and it would spit and sputter, wouldn't start one day so changed the pump and it started but still spits and sputters when its under a heavy load. Haven't changed the cam or crank position sensor, pedal assembly, intake gaskets or injectors. Its giving me a flashing p0300 when going uphill but them it turns off when I'm back on level ground and no extra stress is on the motor. Passed smog like a champ 4 months ago. No clue what could be going on.