96 chev Camaro

Hi, i'm stumped with my cars problems and looking for any insite to what to try, heres the info.

96 camaro, 3.8l 6cyclinder engine 57k miles, idles ok but seems to have a miss sometimes and the ammeter flucuates when the miss happens. Under driving conditions trying to accelerate the car stumbles and misfires and has no power. Replaced the ignition module, coils, wires and plugs. Fuel pressure checked and is nominal, new fuel and air filters. New mass air flow sensor. Have had it on a diagnostic machine and no error codes, am totally baffled at the moment as to what the problem could be, any info is appreciated.

update: checked the alternator and it was weak and soon to be done, replaced that also as of today 4-2-06