So last night on Discovery Channel was a rerun of Myth Busters that first aired on Nov 16th. Found this one interesting because they tested the "drive with your tailgate open to increase fuel efficiency” This myth was busted. It actually decreased the gas mileage by like 30mpg. The explanation I don't remember the details of, but something about where the wind gathers in the truck because they way the truck is designed when the tailgate is opened the air "bubble" doesn't gather like it's supposed to and it actually creates more drag on the tailgate.