Your payload is artificially limited on paper because of the class 2 max 10k lb GVWR. Check your axle and tire ratings and as long as you're within that you should be good to go. You probably have 6500 lbs of RAWR to work with and over 7000 lbs of tire rating, unless you have base 17" wheels which isn't likely with the CTD. You do have to take passengers into account.
Your truck would handle a 14k lb fifth wheel fine. You might find that it handles a bit better with bags or Timbrens but you can figure that out after you hook the trailer up and give it a try. I don't need Timbrens on mine but I do find that they improve the loaded ride a bit, particularly handling bumps at highway speed.