When I was looking a new pickup in 1998 I looked at the F150 and the then-new Powerstrokes with the 7.3 turbo diesel. Figuring 4 mpg difference, and the costs of fuels at the time, it would take about 150,000 miles to pay for the extra cost of the diesel. Eventually it would have been a much better payback, after gas prices rose.
Dodge is supposedly claiming up to 30 mpg in their diesel, which I assume is for a 2wd, running at 55. Figure less for a 4wd, running 75
Now, with all the urea and expensive diesel, I'm not sure you could pay for the engine with fuel savings alone. You definitely can't pay for the truck with fuel savings alone!
I have a 2.0 Ecoboost in my company car, an Escape. It gets a little worse than predicted on the highway, about 24.5 mpg, but not bad for the size of the vehicle. Around 20 in town. Good power, too. When my 04 F150 hits 200k, I might think about another pickup, but I'm thinking the 3.5L Ecoboost will be my choice, assuming they have a good reputation by then for reliability.
Many years ago Winnebago built some small motorhomes with small Renault turbo diesels, and the things were a disaster, seldom lasting more than 20k before blowing up or needing opverhauls. I'm real curious to see how small turbo diesel engines fare, as far as durability, even given synthetic oils and the like.