Are you getting any trouble codes?
Are you able to verify fuel pressure once you put the key to On, and then a few minutes afterwards?
Some good things to do until you can check for codes, and the fuel pressure would be to get some MAF cleaner and clean the MAF'* thermistors, also be sure the tip of the MAF is not coming off and spinning around in the throttle body bore, it does not happen a lot, but it happened to me a while back, and I had to push the pedal a few times to get it to start.
Before suggesting anything else we need to know what the fuel pressure is.
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA