Co-worker has a 2011 crew cab short box 4wd. He told me he gets 15 city and 18 highway. Only 8-10 towing but that's in the mountains out west.
The newer 6.7s seem to do okay on fuel. Not probably quite as good as the others but pretty close. My dad has a 2000 7.3 supercab short box 4wd that has the advantage of being a lot lighter plus no emissions, and it doesn't do any better. Great truck though, and it's only got a little over 100,000 on the clock. He bought it new and it'll be the last truck he ever owns barring an accident.