Since I tow with one of those fuel thisty Ford 6.4 diesels and only get 10 mpg empty, I get as close as I can to a tractor trailer, have the wife hang out on the running board, and when I get close enough she throws a BIG hook at it.
Gotta save fuel somehow!!!
Let them big boys pull me along. Truck doesn't care what it carries, 10 empty, 9 towing a Thunderbolt fiver. Fuel additive makes no difference either. Truck also cares squat about how fast I go. Best I ever got towing was 10.1, worst 7.7. Only thing that seems to affect it is type of fuel I put in.