Engine misfires

:banghead:
2002, 5.7 ltr,1500 savanna, 60000 mls
engine misfires and thus lacks power. obd confirms several misfires.
changed plugs. getting sparks on every plug. checked gasket on intake, seems ok. cleaned distr. cap. stil misfiring.:runaround:
any ideas? help would be much appriciated.
Thanks

Check fuel presure for starters 60-65.

Thanks for your answer. Forgot to mention: My engine runs on LPG or gas, and misfires on both. But wil check anyway

put new parts in : rotor, distr. cap. Tightened intake manifold.
Runs ok whwn cold on idle. slow driving is ok but as soon as throttle is pushed down engine makes a choking sound and doesn't deliver power.:nono:
maybe advancing doen't work ? How to check this? I'd like help with this so I won't have to keep on replacing parts without knowing wheter this is necessary
HELP !!