Adding link to a study on truck aero configurations... Study looks like it could have been written for a 3rd gen ram. Did you know our trucks are the only "aero" shaped trucks back then? Look at a side view of the cab (4th gen trucks have this as well), the back of the cab slopes slightly. If you extended that out it would start to form a tear drop shape. Same with the bed of the truck, it is also not square and tapers off the farther back it goes.
If you look at the newer trucks you'll see they are all starting to take that shape (not sure of the bed but the cab for sure). The newer Toyota Tundras definitely have taken on that shape.
Tailgate spoiler... If your not a fan not much can be said however it does aid in the airflow off the back of the truck. Look at all the newer tailgate designs...
Truck aero study
http://people.cst.cmich.edu/yelam1k/...7-155-1-DR.pdf