I have owned ford cars and trucks, since I first purchased a vehicle. Some 38+ years.  And I have had diesels from 1986(6.9L) and every diesel option offer since, 7.3L(times 4) and 6l upto the new 2012 F-350 6.7l  I currently drive.
This new 6.7 is without a doubt the best diesel ford has every offered.  I drove it on an 2400 mile trip the third day I owned it, I drove mainly 67-68 miles per hour, at this speed I got between 22.8 and 24 miles per gallon.  On the 2 lane highway at speeds of 55-58mph I get 23-26.7 miles per gallon.  And pulling my horse trailer(28foot) with 4- 1900# drafthorses on it, I get 13.7-14.4 mpg.  And I have not found a hill it won't fly up even with a load.  My cousin was so impressed he went out and bought one , and he get the same mileage I do. 
Last fall we went camping with a large group ,12 other campers, they all had new Dodge 3500 diesels and Chevys too. I Sat around the fire one night and listen to them complain about there fuel economy(9-15mpg), and how they are tryiing to buy add on's to booster there mileage.  I finally could  not take it any more, so I told them what my 2012 6.7 does and suggested the just buy a Ford and solve all there problems.  One man there thanked me for the info.  because he had ordered a new 2013 F-350 6.7 and it was coming in to his dealer on the next week.   There was silence at the campfire for about 5 minutes.   Anyone who does believe in this 6.7 just drive one and you will see.