Max GT

Hi I am new in the forum and I have the same problem. My car is R33 GTS-T 25T Series 1 Auto. I recently increased boost to 12 pounds and started to experience misfire only at full throttle (the car has a pod filter, cat-back 3" exhaust, Unichip, bleed valve and standard everything else). I took my car to Nissan yesterday and fitted a new set of standard heat range 6, NGK Platinum plugs (previously Greddy Iridium, heat range 7), which improved the misfire problem a bit. However, idle rev has gone up from 660rpm to 760rpm. Any thoughts will be much appreciated.