[99LeCouch]

A good first step would be getting the factory undertray. GM did their homework with that part. It cuts down on drag via shunting air underneath the car instead of at the engine block. Mine was off for the past few weeks, and man have my glides on the highway gone poorly! The car also seems to wander more with it missing.

I'm planning on adding some Coroplast on either side of the factory part to block off the front wheel wells. The factory chin spoiler on my car isn't deep enough to block air coming just underneath it from hitting the front suspension components, and ultimately the back of the wheel well.