I'm also currently in the process of the big "switch-over" from a travel trailer to a 5'er. Just got the new tow vehicle, which will pull about ANY 5'er that we'd be looking at, and installed a front hitch mount on it. Both Yakima and Thule make a front hitch "Y" post that will hold the front bar for our kayak rack. The back bar will mount on the cab, where the front cab bar would normally be placed. This will allow us to carry our three 'yaks, and tow a 5'er.
So, as you can tell from the updated sig, after more research and test drives, I went with the 6.7L Cummins. Not being sure where DW wanted to go with new 5er, didn't want to come up short on tow rating. The 17,100# that the Cummins provides gives me endless possibilities.