Air Intakes

Kodiak's are known having good air intakes. If you are referring to K&N or similar. They have not made a replacement for the 2007 and newer Kodiak's.

Your right until I saw this unit listed below

http://www.carid.com/2008-chevy-kodiak-air-intakes/volant-air-intake-346720.html

Not sure where you would put it. I would want to see one installed before I would spend that kind of money.
Back to my original statement. Our Kodiak's have a very good intake. Unless you have a engine that is trying to put out 500 hp. :R

Best way to get better mileage is to slow down.

If one can improve the effecency (spelling?) of the eng it will make more power with the same amount of fuel. See the mods in my sig and I get much better mpg towing than stock. Just increase the output then let your right foot do the rest. I would never use an oiled filter on a diesel. K&N's have dusted a lot of boosted engines.