*grin* It's a diesel, ain't no such thing as _good_ fuel mileage. Though better than towing with a gasoline engine truck; we should get roughly 10-12 mpg towing vs 6-8 mpg for a gas engine.

What the extra tank gives you is flexibility, to be able to do a long day's drive and then fill the truck at a regular gas station after setting up the trailer, rather than needing to use a truck stop while towing. Or the ability to pass up dodgy diesel and drive a hundred more miles to a station you know is reliable; that sort of thing.