I'm about to move from DC to Vegas soon and I am looking into increasing my fuel efficiency in any way possible. My personal vehicle is a Toyota Tundra, and my wife's is a corolla. I've been playing with a few configurations for the trip in my head that involve towing the car, driving the car behind the truck, driving the car in front of the truck to cut the air ahead of time, and several different aerodynamic configurations for the truck itself (bed covers, spoilers, tailgate positions, etc.). So far, all of the different configurations have been in my head, though, and I was wanting to do some simple aerodynamic simulations on a computer to figure out the best possible configuration. Are there any Python plugins that I could use that would extend the fluid dynamics simulations in blender that would allow me to get some straightforward metrics on drag and streamlining?

You are looking for some sort of computational fluid dynamics package. I would check for something in SciPy first.