Don't want to piss anyone off, but diesels getting crazy high gas mileage does not happen either. Yes they do get better than gas. Too many guys use the overhead lie-o meter. Everyone needs to get out the pencil and paper and come back to reality.
first gen cummins do very well in the 20 range, and since I'm in canada my fuel measurements are different
there is more quarts to a gallon so its very possible to get 29 MPG canadian especially since the truck I was talking about was owned by a diesel mechanic and was tuned for MPG