Just put a K&N Aircharger (#67-3059 I think) on my 05 GXP and with the resonator deleted it can really set you back in the seat on WOT. Throttle response seems alot quicker and I've noticed about 1.5 mpg improvement. The instructions were very clear and every little detail was exactly as described, so I think you can get one for your 05 without worry!