If you do purchase a new diesel the first thing that you need to do is delete the DEF, DPF, and EGR systems. The truck will get a lot better fuel mileage and you will avoid three separate costly problems.
Just bought a 2015 Ram with the 6.4l hemi. I tow a 29ft tt at 7k or so. Did really well with a trip out to southwest Colorado. 10-11 average mpg. 2nd gear up Monarch pass with no issues. My decision was weight of tow and cold weather. I sometimes have to leave my truck 3 or 4 days with no way to plug in. I also like to hunt 3rd season and don't want to worry about starting in the backcountry. Really like the truck so far.