The difference in the cost of fuel is not an issue if you think about it.
I believe most folks use premium in their gas trucks while towing and the delta between gas and diesel is very small. The real issue is how much you use your truck for towing. The more you tow and the longer you plan on keeping your truck; the more the diesel makes sense.
For the purpose of this example I will use regular gas and diesel prices off the sign down the street.
20 gallons of regular gas @ 3.89 = 77.80
20 gallons of diesel @ 4.17 = 83.40
A "delta" of $ 5.60
Now drive that 20 gallons @ an average MPG of 9 MPG gas truck and 12 MPG diesel truck.
Gas truck = 180 miles
Diesel truck = 240 miles
The diesel truck goes 60 miles further on that fill up. The $ 5.60 you saved at the pump could have bought you an extra 1.44 gallons of gas. This would have taken you an additional 13 miles.
So if you add that to the 180 miles for an apples-apples comparison, you get 193 miles on an constant dollar basis. So, with diesel you basically get 45 miles "free" with every 20 gallon fill up.
Now, the diesel will cost you about 6,000 dollars more in a new truck than the standard gas engine (about 4,000 more than the V-10 option).
At an average cost of $4.00 a gallon now, 45 miles @ 12MPG saves you 3.75 gallons or 15 dollars per 20 gallon fill up. If you fill up once a week; every week; that is 52x15 dollars or 780 dollars saved per year (this has to be offset with higher maintenance costs for diesel engines of say 200 dollars more in oil and fuel/oil filter changes) or 580 bucks in savings.
You would need to operate the diesel truck for 10 years to break even on the standard truck/diesel truck comparison and 7 years on the V-10 example.
Non-towing the mileage is about the same city/highway so the diesel does not pay if you don't tow. Now, 20 miles a week average towing is pretty low for most of us. The more you tow the less years to break even.
Also this is also based on 4 dollar average cost of gas/diesel. If fuel prices go UP and the delta between regular and diesel stays relatively the same; payoff in years plummets the fuel cost climbs.
I have ignored "driveability and towability" as well as "easier to find gas pumps than diesel pumps" and many other factors that go into this tough decision. If you trade your truck after 3 years, diesel does not make sense at all, IMO.
Besides diesels are just "cool"
and who can put a price tag on that?