You might want to check out automotive internet forums for vehicles that use the same engine as yours and then search those sites for similar problems. Maybe something like www.chevroletforums.com
and there are a bunch of others.
Aside from you checking the fuel pressure with the dodgy gauge, have you done anything else with the fuel system? To me it seems like you've kind of ignored the fuel system so far. I think that some of the 5.7L Vortec engines needed around 50-60 psi for fuel pressure.....are you 100% sure that 30 psi is what this engine needs? I don't know the answer, just throwing out some ideas.
Cheers & good luck!