What I'd really suggest is just going ahead and putting on the OEM Class IV hitch. It's a bolt on application. You will probably need the relays too. Try this page for the relays. They're at the bottom. http://www.courtesyparts.com/titan/towing.html
There's a class III hitch on that page too, but I really would recommend the Class IV.
The dealer package comes with the relays, and isn't much more than buying from other places. I bought mine from www.etrailers.com then had to go to the dealer and get the two relays for about $50.00. Ended up being around $225.00 for everything. etrailers is a good web site and they deliver fast.
Class III hitches are normally rated for towing 5000 lbs and 500 lbs tongue weight. Class IV is higher, on the Titan, to go over 5000 lbs, you need a weight distributing hitch to go into the Class IV receiver and the extra bars that go with it to attach to the trailer frame. Setting up a weight distributing hitch/trailer is quite a bit more complicated than a Class III rig; it would probably be a good idea to work with someone who has experience if you go that way.