I've got a 2012 Chevy with same motor and gears. Did a lot of searching for a 5w TH last winter... Slim pickins' for sure. The rule of thumb I came up with was if the 5w has 3 axles it's too big for that truck. And any 5w TH you get is going to be pushing your tow limits. I'd advise you to get to the scales after you pick up your new TH and make sure you know what your loaded tow weight will be. You WILL be close to exceeding your towing limits, especially if you're hauling a Roadglide and Grizzly in the back. Options like the drop down queen beds in the back add a bit of weight, if you don't need them, opt out.
That said, look at the Torque 301 and the Raptor 300MP. Good Luck!