dam air
When I bought my 2002, it was a $22 factory option, but my truck didn't come with one, or a hood liner, or rear wheel well liners, blah blah blah. :{
The purpose of an air dam is to increase fuel mileage by reducing air turbulence (drag) under the vehicle. It could improve handling (tracking and steering) at speed by creating more down force on the front end. That's how it works on race cars anyway.
There is a vendor, I think it's the maker of Air Bully Dog Hoods, who makes a cold air intake that routes to a custom air dam that is much bigger than stock. I spoke with a member at May Madness who has one. He said it felt like his truck handled steadier, eg. required less steering correction, while freeway cruising.
All those body bits I didn't get from the factory are on my wish list. I figure someday I'll salvage them and maybe some factory tow hooks too. Then I can cut holes in my air dam to mount the hooks. At least 90% of the trucks I see have air dams. I would think that if they did anything to improve fuel mileage, the manufacturer would want them on in the interest of meeting CAFE standards. Maybe DC saving the 22 bucks today is more important any potential future savings for the truck owners. Nah.
Neil