Here's what I did. I first bought a K&N drop in for my 01 at 5k and stayed that way until last June when I bought my Gibson system at 75k. Not much of a noticable increase in power or mileage but sounded nicer when hitting the powerband. Three months later I got the Volant intake and noticed a little more get up and go. My advice if you can only get one thing at a time is to get the exhaust first. IMO getting the intake with the stock exhaust doesn't make sense as you add more intake volume but lose it trying to move the extra air through the restrictive stock exhaust. Can't really say how much added mpg I've gotten with my setup as I've added 265/70R16 Dueler HP tires with are taller than the 255/65R16s that came stock and it seems that my ODO is now off a bit.