I would recommend staying away from the first year of any truck design change if that included an engine or transmission change. I would also recommend staying away from the first year that DEF was added to a diesel truck. Specifically, I would stay away from the 2011 GM trucks. Lots of issues with the DEF system in general. You might find those around cheaper, but I would stay away even if the system has been replaced. Spend more for a 2012 or go back to an older year just to get better reliability.
Finally, based on your weight. Do yourself a favor and get a 1 ton. A 3/4 ton can do it, but you would be on the edge and thinking about upgrading your suspension. Just buy the right truck from the beginning. I have a 2015 3/4 ton Chev and love it. It pulls my trailer great, but at 12K or so, it is heavy and I wouldn't want to pull heavier without upgrading my suspension. Wish I would have purchased a 1 ton long bed from the start.
We bought the newer model Chev due to how quiet the engine was. My wife used it at the time as a daily driver and was not going to drive a noise diesel. We test drove all 3 brands and the GM was the quietest with the Ford being close. The Ram was very loud and she got in it and said no way... I was ok with the Ram as I know the Cummins engine is a good engine, but the Duramax Allison combination is also a great engine transmission combination.