I've got a 2015 Ram 1500 Big Horn with the EcoDiesel engine, stock gearing and 20" tires. Only just breaking it in, its got about 2000km on it and so far 10.9ltrs/100km is the average. This is with mostly city driving and some hwy, I'd say 80% city and 20% hwy, don't have exact calculations for the split though.
That is incredible mileage! My HHR gets anywhere from 8.5L-9.1L/100kms combined depending on the season etc. For a half ton truck to get that fuel economy is really something.