I have an 02 silverado with the 4.8 v-8,
I added JBA headers, and a 3" cat back exhaust with 2 chamber flowmaster, stock exit single exhaust, this is supposedly the best setup, for performance gains
also I have the FIPK K&N filter and Superchips programming, before I added 4:10 gears, I could get 23 MPG on the highway.a few months ago, I got Bilstein shocks, front and rear, great improvement.