Mex: That is the first time I have seen anyone stating that ULSD gets lower mileage than say LSD. 2007 to 2010 ( no DEF) do get lower mpg than say a 2004 truck. But that is due to a lot more than just the fuel. Newer trucks( 2011 and up) are getting better mileage than pre emission vehicles. BUT they have so many emission system problems the fuel savings are quickly canceled out! Mexican truckers with those old Dina trucks will have pump seal problems with ULSD. Our Old Bluebird loved Mexican diesel. High Cetane!
Moisheh