For what it's worth, keep in mind that the Jeep Wrangler places dead last on Ecomodder's list of drag coeffients--so it's got a lot of room for improvement:
Vehicle Coefficient of Drag List - EcoModder
Also, as has already been pointed out, keep in mind that driving style will play a big role. Faster speeds = aero plays a bigger role. This chart illustrates that:
The chart is for a semi truck, but the same concept applies.