I have a 2500 HD DMAX, 2002, and drive it in England.
I can say it does 27mpg on a 100 mile motorway trip @ 70-80mph,
or 22mpg dodging around.
I know many 4x4 owners who get less from their 2.0L diesels.
I would never swap it. I want a fifth wheel camper to haul, but need to get one from States ??