Someone told me the samething about the mythebuster thing. But I have found driving at 60 mph without the tonneau cover I got anywhere from 12-14 mpg. Now doing the same driving with the tonneau cover on I get 14-16 mpg. Thats why I believe a tonneau cover is better. I have seen somewhere I forget where I seen it but it was a test to that showed air that would do a circular motion then drop into the bed and make the tailgate act as a sail. I will have to look for it. I dont it works for me on gas mileage so I guess thats all that matters. Also I always use the a/c cause I hate the wind noise but they say if you are on the freeway you get better mileage with the windows up and the a/c on. If you are driving 55 then the windows down are better. I dont know how a/c can effect the gas mileage really but thats what I have heard. I guess certain things work for certain people I guess.