2007 Ford Mustang 07 Mustang Misfireing P0300

Engine Performance problem
2007 Ford Mustang V8 Four Wheel Drive Manual

I replaced MAF and O2 sensor. The car has a supercharger on it and when it is pulling hard between 2500-4500 RPM is starts to misfire. I you don't get on the throttle it runs smooth. The higher the gear the lower RPM's it misfires at. It also just had new high flow cats put on. This car should have 450 hp and runs like it has 150. It has 9500 miles on it.