I drive a 2002 Chevy Silverado 2500 HD 6.0 I love it, but it is a gas hog!

I am looking to improve my gas mileage, torque and overall performance. I am thinking of buying a tuner and a cool air intake. I wanted to get some advice on what products people recommend. I am leaning towards the Diablo Tuner and the K&N Air Intakes. Does anybody have any suggestions for me? Thanks for the help.