Just added a K&N Airfilter. I normally fill at a half-tank and it looks like the mileage is up by about 1 mpg to ~21 mpg. Slightly more intake noise, but not objectionable. It installed easily, but you do have to be cautious to get the sealing rib aligned in the air box lid. The K&N edge molding is more floppy than the OEM air filter.

 

What kind of mileage are you getting?

We averaged a little over 18 mpg with our 2007 diesel shorty.

 

Only problem with running a K/N air filter is if you don't keep it clean and oiled every couple of thousand miles dirt will get through it into the turbo then you have big problems. If your still within factory warranty and you have a turbo failure and they relate it to the K/N because they can see where the turbin has been sand blasted so to speak the warranty will not cover the repairs needed. Food for thought.