I will wait until some real people own XDs and actually put some mileage on them before I pass judgment. The mpg estimates so far are not very accurate seeing as none of the test trucks have any real mileage on them. Diesels take awhile to break in. Most diesels will show improvement in mpg by 10,000 miles and plateau around 50k miles. So running a test loop with a brand spanking new low mileage Cummins is not the most accurate way to predict where the truck will ultimately wind up. Gains of 3-4 mpg can be common. So figure that most tests show around 17mpg in various conditions, the XD could very well wind up around 19mpg combined when all said and done. There could also be some programming in the ECU that can contribute as well. I can't verify it, but I have heard new low mileage diesels will tend to regen more frequently during break in thus using more fuel.