Has anyone put a K&N Filter in your truck, and did it increase your gas mileage significantly?

It will add Hp to your truck either way! try it and let us know

This is very late and I hope you read this. The K&N filter did not help for regular highway driving, but it did help when towing my boat where I was getting just over 13 mpg. I now get around 14.5 after towing the boat 5 times on a combination of interstate and 2-lane rugged terrain roads. The boat and trailer go at about 3,500 lbs. (The Titan outpulls my 2004 GMC Z-71 1500 easily).

This is very late and I hope you read this. The K&N filter did not help for regular highway driving, but it did help when towing my boat where I was getting just over 13 mpg. I now get around 14.5 after towing the boat 5 times on a combination of interstate and 2-lane rugged terrain roads. The boat and trailer go at about 3,500 lbs. (The Titan outpulls my 2004 GMC Z-71 1500 easily).

What was your gear ratio on the GMC and the Titan.. that will make a differance too.
Make sure you are comparing apples to apples