THis weekend before we took a 4 hour trip i decided to try out the K&N drop in air filter. I read about it not helping that much. I had it in my 01 4.6 and didnt really pay attention to the mpg but i was really suprised. When we took the same trip last month i got 14.5 mpg. I have a 5.4 xlt reg. cab. Terrible i know right! My dad has the 4 door lariat (2004) and he gets 16 mpg. Anyways we got exactly 18 mpg on this trip. I was definitely suprised. Ive never got over 15 in this truck and now 18. I guess it does work? I would get the AF1 but i had the K&N FIPK in my old truck and thought it was a waste. But i am pleasantly suprised about the drop in.