I have driven many different vehicles with both gas and diesel engines and came to the conclusion over 20 years ago that diesels are meant for towing. Does this mean that their overall operation will be cheaper? No, but the towing experience will be more enjoyable. With the new high power diesels, there is no comparision with the exception of tires. A gas engine vehicle will get more life out of it's tires because it doesn't have the torque to peel the rubber off like a diesel. As far as mileage goes, if you drive the same trailer at the same speed, the diesel will get a little better fuel ecomomy than the similar gasser, but add a head wind, or lots of hills and the diesel will greatly out pace the gasser. The other thing about the diesel is you will have the ability to easily maintain the posted speed limit which might not be so easy with the gasser. When the guys with the gassers say they get 10 mpg towing their big fiver, let's have them run it next to me towing my 5er. I will get an honest 10-11 mpg with a gvw from 20 to 26k I have yet to see a gasser that can match this mileage with the same type load. I used to have a new Dodge 3500 with a V-10 and 5 speed. I towed a fairly heavily loaded 20ft enclosed trailer from Worland, Wy to Cheyenne, Wy about 400 miles. Between Casper and Cheyenne running down I 25, I got 3.8 miles per gallon. Nuff Said!