I'm really interested to know about this, too. In my 2006 Jeep Grand Cherokee Overland that I traded-in yesterday on my new TCH, I used a K&N air filter. It almost instantly took me from an average of 15 MPG to 17 MPG (hey, two MPG on a Jeep is a HUGE increase), so I'm really curious about how the TCH would behave with one.