did you remove the resonator in the exhuast system? remember with the KKM you are allowing more air flow into the engine. so what goes in must come out, however with the stock resonator in place this restricts air flow, i am thinking you are not getting proper exhuast flow. a very common mod is to remove the resonator, and it is cheap! bear in mind it will change the sound of the exhaust. also make sure your engine isnt running hot, i hear installing the KKM and not removing the resonator, the engine may run hotter?
good luck!!!