Help!

I have a 96’ GT with KN intake and Off-Road X-Pipe. Recently I have been having a problem when the car is under a load and it feels like the engine is getting to much fuel then misfiring or something. When I accelerate at a moderate pace it will rev fine but when I hammer it, it will stutter and you can here the exhaust drone. I have checked the plugs, plug wires, O2 sensors, and I listened to the injectors to see if they were all working properly and they were, but I could only check them at idle speed. Any suggestions on what to do would be greatly appreciated. Thanks

I checked my codes last Sunday and the only thing reading is for mt O2 sensor because I have an X-Pipe. I recently changed my fuel filter last week but the old one was really nasty. This may have started the problem but it seems to be getting worse.