Saw this article from Consumer Reports on the new 2.7L EcoBoost. Seems to fall in line with what you've been saying, Padgett. The consistent conclusion is that you will get better mpg towing with a diesel, but you may never overcome the initial higher cost of the diesel, especially when considering the price differential between diesel and gas. I did like that the Airstream used in this example is close to my tow weight for my 3124KS.
I'm still at least a year away from buying a new truck, so I'm sure there will be lots more to think about by then!
http://www.consumerreports.org/cro/n...-tow/index.htm
Dave