Towing 16,000# Gas 6.9mpg, diesel 10mpg 116,000 miles needed towing to pay off the diesel upgrade Empty Gas 16mpg, diesel 19.9mpg 650,000 miles needed to pay off the diesel Video
I don't consider fuel costs into the equation because it changes too much. Over my years of diesel/gas use, sometimes diesel is cheaper, sometimes not. It isn't really an option to trade vehicles everytime the fuel cost advantage changes. The diesel fuel economy advantage is always there though.
One time we had a statewide gas shortage. Diesel was readily available though. Once in awhile having multiple vehicles with gas/diesel capabilities is nice.