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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

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.
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Sounds fuel or compression related. Have you checked compression or performed an injector drop test?