I have the same truck but in the supercrew (157" WB) which reduces my towing to a max of 7500 lbs. We have been on one trip (1300 Miles) to TN and back with no issues. The truck pulls it fine but you know you are pulling something. It pulled the hills without any trouble, as long as you don't expect to climb them at 65 or 70 Mph. My trailer loaded is around 6700 lbs with a tounge weight around 800 lbs.
I would imagine it would be a more pleasent experience if I had a 250 but for now it works just fine.
Make sure you go and weigh your setup. Weigh the truck alone. Truck with trailer (no wdh). Truck with trailer and WDH hooked up. This is really the best way to know that you are getting the most out of your WDH.