how much fuel pressure does it have when turning the starter?
so...it wont start when it is cold.........but does when it is hot...correct?
how do you get it started the first time?
again..you need to check the fuel pressure,,,these must have no less than 60psi at all times...even while turning the starter when it wont start,,,it is very common to get a bad new fuel pump for these vortec engines,and it may need to be replaced again...so check the fuel pressure first,,again,no less than 60psi..
if the pressure checks out,,check for a spark on the plug wires when it wont start,,sometimes a bad ignition module may not give a spark when the starter is turning...also,if it hasnt been done,,give it a tune up..new plugs,wires,rotor and distributer cap..these caps and rotors can burn up on the inside and cause a similar problem,even if they look new....
but,i still think your problem is in the fuel pressure
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Notice: Do not allow the fuel pressure to exceed 517 kPa (75 psi) . Excessive pressure may damage the fuel pressure regulator.