2002 Chevy Camaro Misfire problem?

[BrandnM]

I posted about a week ago and got some great advice, although after several repairs I am still having a problem. Maybe someone will have an idea. I have a 2002 Camaro 3.8l with 80k on it. I have never had any issues with this car at all until last week when I was driving home, whenever I would go into passing gear the car would miss and SES Light would flash but the second I would let off it would quit flashing and run fine. So the next day I changed the plugs as they had about 30k on them and also they were replaced with non-iridium plugs when they were changed at 50k. Car ran better but still would misfire and flash the SES under a load. So I replaced the plug wires. Again, car ran significantly better and even under a load the SES wouldn't flash until the day after when I was going up a hill it did the same thing. After cleaning my MAF Sensor, Intake, Checking for leaks in the intake and such I found that my belt was in need of replacement as was a the belt tensioner pulley. Also I have no air system leaks. Another thing I had seen online was to check the fuel filter. Well it just so happened that my fuel filter had never been changed it was the factory AC Delce fuel filter. The filter was so clogged that i could barely pass any air through it let alone fuel, which was suprising because the car ran decent for having such a dirty filter. So I was HOPING that filter would fix the issue, well the car started, smooth, tons more power, just much smoother even under a load and coming up a decent sized hill in passing gear. So i decided I would run it a little harder to make sure it was fixed, sure enough when i manually shift it and bring it close to redline (I didnt redline it) the SES Started flashing and the engine felt like the power was reduced. So I pulled over restarted the engine and it was fine, drove all the way home with no light and smooth as can be, it seems be very intermittent and only when I really get on it. The only thing that I havent replaced in the ignition system are the coils, i would really appreciate anyones input as to the cause. I would just take it to a shop but ive put so much time into it and hate paying a mechanic for something i can do myself. Most likely I will buy the coils tomorrow and hope that fixes it. Im really hoping its not something like a MAP or O2 Sensor although the SES light doesnt stay on so is there even a code for Checkers or Autozone to read if I were to go there? The very first time the SES Light flashed it stayed on, then I replaced the spark plugs and it seemed cured so I had the code cleared i dont know the codes numbers but I know it was a misfire from cylinder 5. Coil? Injector? Fuel Pressure Regulator?