If your looking to add a little "performance sound" to your truck, and are short on funds, then just take the lid off your air box. Once you step in it you'll definetly hear a difference, you can hear the intake sucking in the air, mainly in the upper RPM range. Putting a K&N, or other hi-flow filter will increase the effect. I have the K&N, and it is pretty loud when I mash the skinny petal!

I know that this isn't a big secret or anything, just spreading the knowledge.