Improved gas mileage?

[gfunko]

I wanted to see everyone's opinion on this and see if it really made a difference? I have a neighbor who has a Chevy Sierra (not sure of year but from 2003-2006). He claims to have improved gas mileage by changing to a K&N air filter and his exhaust from the headers on back. While I know it improves on how your vehicle breathes, does it really improve mpgs?

Obviously, owning one of these trucks, having GREAT gas mileage is not the utmost concern of mine, just a question I'd thought I'd ask

 

[Blazed]

Theoretically if you could keep your foot out of the pedal after adding those things yes it would help. It would only be 1-2 MPGs tho and there's no way you won't give it more gas with those awesome sounds coming from your truck.