I think you are having the same issue I did a few years back. My truck started having an occasional hard start condition where I had to crank it 2-3 times, and then it would still be very hesitant to start "strong". After some diagnosing with a fuel pressure gauge, I found that the pressure would quickly bleed off with key on, engine off, after the pump finished priming. I paid the dealer $1,100 to install a new fuel pump, but it came with a lifetime warranty if it ever failed again so I figured it was worth it. I believe that was around 160k miles (approx 7 years ago), but I'd have to check my records to be sure.
Turns out, the fuel pressure regulator was failing and allowing pressure to bleed back down to the fuel tank after the pump stopped priming. Sucks that, for my year model at least, the FPR is build into the fuel pump assembly. If I owned an earlier year model GMT800 (believe 2000-2003), the FPR would've been right on the fuel rail and easy/cheap to replace.
Either way, I hope the new fuel pump fixed it right up! It solved my problem, and I suppose it will solve yours as well.