If it were me and I was going to be pulling that weight and living full time, I would pick up a lightly used 2008+, 6.7, drw Ram. Having owned a 2006 5.9 that was a great truck, the 6 speed transmission and exhaust brake that come with the newer trucks are great. The 2007.5-2012 6.7 is a fine engine, but it doesn't have DEF which can create emissions related issues if the truck isn't worked. At 14k lbs you're going to be working the engine so I wouldn't be too concerned. If your budget will allow, take a look at the 2013 Rams, they have the newer ace technology and achieve better fuel mileage because of that.
