Auto Gear Kustomz

I have a 1998 GT with the 03 heads on it and was wondering if there is a certain plug i should run and degree. I'm kind of new to the 4.6 life and alittle clueless..
Also lately my car is starting to backfire out the driver side. When you take off at a good acc. and then let off alittle you can hear it in the driver side of the motor...also just started being real slugish on take off.. any ideas