Drafting can mean mpg improvements, but I've never understood the logic. For a few dollars saved per year, there's a BIG risk of a broken windshield, chips, and dents. (Trucks throw lots of rocks and debris). Fixing some of that, one time, will cost more than any gas savings. The truck is also a visibility barrier, causing a big safety problem. I try to stay well away from trucks, following further away than I would follow a car.