They say it helps keeps more air going into the grill area , than under. But the trucks are soo high I can't believe it makes that much of a difference. And if it really did , it would probably be part of the tow package, but it aint.
My conclusion has been that it's for looks.
Now on a slammed Dak or something, winding through the Glen Rock, it might make a difference. .
Some folks buy them aftermarket or from DC... you may find a taker for it.
Bob