It's a lot of money you'll be forking out. I drove all three before writing the check. I am partial on the Cummins because it gave me what I wanted. I read things on the Power Stroke Forum that steered me away from buying that, I didn't like the look/feel of the 15 Dmax, and as said above, the 3500 Ram fit the bill for me like a glove.
6000 miles on my second CTD and I love it more and more every day. Mine is a DD as well, so I opted out of the DRW, but based on your trailer weight, thats what you need. If you read on the forums, all 3 have their good and bad, none of them is perfect.
Best of luck with the purchase.