Before you pull the trigger on a hitch, I would strongly urge you to take a look at the Reese Goosebox.
Of course, you also need to get the gooseneck ball setup...my truck (see sig) came with the B&W Turnover Ball already installed.
I was so glad to be rid of the large (and heavy) hitch in the bed of the truck!!
I towed with a short bed Ram 2500 (MegaCab) and a PullRite Superglide auto slider hitch and a MorRyde pinbox. Both are excellent products and worked flawlessly for almost 9 years of towing.
But the Goosebox is so nice with suspension to cushion the connection to the truck (airbag and twin shocks) and the added convenience of having the truck bed available is totally worth it.
The stability is excellent...of course the dually with auto leveling rear suspension helps with that!
My dually is a shortbed MegaCab so just to be sure I have enough clearance I went with a B&W offset ball which moves the connection point (the ball) back 4 inches from the ball socket.
Didn't need (or want) a long bed, but LOVE the MegaCab dually!