for me in pick up it was a major improvement....and about gas...i have no idea about that...dont really pay to much attention....but its def better then stock and or what you can get at the autoparts store.i know it adds like 5-10 maybe more horsepower...and you dont have to replace the k and ns...just wash recharge and your good to go
Anyone who buys this (heck of a deal! Just wished I owned a GM so I could buy it.) should expect some better milage, slightly improved performance, but perhaps the most important thing is it means you wont ever need to buy another throwaway $20 air filter because its reusable.