the problem is the fuel pump...you need to check the presure,these must have no less the 59psi at all times,even while you are turning the starter,,,i would think your presure is a little low,,,this is a common problem,,,also check the presure of the new pump before you install the tank,it is common to get a bad new pump
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Test Description The numbers below refer to the step numbers on the diagnostic table.
Notice: Do not allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel pressure regulator.
it wont be..lol..these vortec engine are real hateful about the fuel presure...like i said..it must have at least 59psi even while you are turning the starter