Misfiring Plugs? Skyline R33

[bzd82]

Hi guys, i have a r33 skyline auto with basic mods, cooler, full exhaust, splitfire coils, platinum plugs, pod filter, bleed valve, running 12psi. i have had these platinum plugs in now for about 10000kms with no problems at all and i carefully gapped them to .8 when i installed them. lately i have put a turbosmart blow off valve type 3 atmo vent, and my mechanic friend and i done the timing belt. but now everynow and then my car will misfire when i give it some. does anyone know why its doing this? is it the plugs? its been running sweet with these plugs last 10000kms, could the blow off valve be somehow making my plugs foul up? i wouldn't have thought so but hey u never know? its done 77,000kms series 2. should i just go get cheap copper plugs and get rid of the platinums, any help would be good? Da.