I was traveling through Nebraska this morning on a very straight and level road and was bucking a head wind. My computer said I was getting 4.5mpg.
I was approaching a slower truck but a car was coming up on my left so I slowed down a little and was maybe 300 feet behind the truck in front of me. I looked down and I was getting 6.5 mpg. I stayed there for maybe 25 miles and no change. I then passed him and as soon as I started half way up his truck my mpg started to go down and once I was in front, 4.5 again.
So I wait until a truck passes me and I catch up about 300 feet behind and bingo, back up to 6.5 again.
That explains why I'm tooling along and I see a truck catch up to me then he stays with me for 100's of miles!!!! My guess is that they are looking for a truck that has the cruise on and matches there truck in the hills.
I'm sure you all know this but nobody has ever mentioned it. I thought it was pretty cool. I'm thinking about putting an anemometer on my truck and doing some experiments. I find this interesting.
Also, a study was just done. During the hot weather it is better to leave your windows open up to 55mph. After that, it is cheaper to run your A/C due to the added wind resistance that leaving your windows open causes above 55mph.