i cant complain about the k&n drop in filter but one of my buddies had on then went to the cold air intake and said he could tell somewat of a diff. but i have a d.i.y. intake and i really like it.
it gives you easy hp. but really cheap.
i think a d.i.y. intake is the best way to go if you are kinda short of money like me.
i know a guy also that has one in a 04" duramax for about 2 years now and not had a single problem
but personaly i would go with a d.i.y. intake since it is the cheapest and ive heard that a d.i.y. intake gives you more hp. and keeps more dirt out, but i dont know from experience