Stock Airbox limits flow. And Dual K&N's on the end instead of the tubes eliminate the CAI effect.

The best options I have found are a V8 airbox with stock tubes, or a 3" CAI with relocated K&n filter. The former looks less tuner, but has increased turbulence and a slight loss of torque. The latter has a smoother flow and better filter location.

I had The V8 Air box and now have the CAI. The airbox cost me around $250 shipped and the CAI I made.

You'll be looking at anywhere form 5-15 hp gain depending on other mods and which you choose