My 2014 Ram CTD 4X4 Towing 17.5K got 11mpg. That was as good as it got. The milage got better at around 16,000 on the clock.
My new Ram 3500 DRW, With the 4.10 gears and Aisin trans, towing the same 5er is getting 10.2 mpg, but the Trans and coolant doesn't get hot pulling steep grades like the 2500 did with the 3.42's .
I run Diesel Clean in the tank now also to increase the Cetane %.
2015 Landmark Newport 365
2015 Ram 3500 4x4, CTD, DRW ,MC ,AISIN , 4.10's,
Six Burning Six Turning ! ,RVM 104