I have kept track of every tank of fuel in my truck since I bought it. Now have around 30,000 miles on it. The lifetime average MPG is 11.12. My truck is a dedicated recreational vehicle - not a DD. Most miles on it are spent towing something, be it a 2500 pound fishing boat, up to 17,000 pounds towing my 5er and ski boat tandem.
It has been down as low as 7.92 MPG towing 70 MPH into a head wind. Best was a short highway run at about 60 MPH when I topped off to see 24 MPG (not something that has happened since).
The 2012 is a great truck overall. MPG isn't it's strong point though.
2012 RAM 3500 Laramie Longhorn DRW CC 4x4 Max Tow, Cummins HO, 60 gallon RDS aux fuel tank, Reese 18k Elite hitch
2003 Dodge Ram 3500 QC SB 4x4 Cummins HO NV5600 with Smarty JR, Jacobs EB (sold)
2002 Gulf Stream Sea Hawk 29FRB with Honda EV6010