Hi I have a 1999 GMC Yukon with the 5.7 liter that I'm having troubles with. I have recently replaced my fuel pump, fuel filter, spark plugs, it has new ignition switch and it had newer cap rotor and plug wires on it. Hooked fuel gauge to it had 50 psi for the prime then dropped to 20 psi while cranking. To get it started I have to jump start it or ether which I nknow is bad for vortex engines but trying to get answers to point me where my problem is. Any ideas is greatly appreciated - - - Updated - - - Also as soon as I do get it started it starts up just fine aftwrwards , but qwhen it sits for a few hours it won't start again.