When you make the intake system lest restive you will see a horspower increase. The misconception comes in that if we publish a 12 hp increase the assumption is that you will see a 12hp increase when driving down the road. This is incorrect. The engine uses a 3rd the horsepower its capable of making to maintian cruising speed. So reality is that the intake system being less restrivtive is going to allow the engine to draw in more air with less effor thus increaseing your engines volumetric efficiency. This simply means you will recieve better throttle response, more towing power, and depending on the conditions a MPG increase is possible.

I know it may not mean much from my because I work for K&N, but I don't believe in baffleing people with BS to sell a product.

I have an 04 f150 with the 57-2556 intake system on it. My buddy has the same truck same year but his is 4 wheel drive. We both noticed the throttle response improvement and he notice the power increase when towing his trailer up the grape vine. His truck did not down shift as early and he was able to go up the grade 10mph faster. He also noticed a 2mpg increase with his I notice a 1 mpg with mine.

Take it for what its worth but you can put a system on with out a programmer and see an increase perfomance and possibly mileage. The reason you don't need a programmer is becaus the MAF sensor and the O2 sensor will work in conjunction with each other to make sure your the engine runs at the Targeted AF ratio set by the factory.