had replaced all coils,ignition mudule,and plugs and still have mutiple misfire. on 1999 Pontiac Grand Am

replaced parts and still the same no power and rough idle

2 answers
Any other codes besides misfires ? Any ability to read live data? Access to a vacuum guage--easy check for valve related problems often overlooked is with an old-fashioned mechanical vacuum gauge.
Sounds fuel or compression related. Have you checked compression or performed an injector drop test?