Here are some links to help you out....
www.trailerlife.com This site will give you the towing capacities of different trucks, both bumper pull and fifth-wheel/goose-neck.
www.rvtraderonline.com You can usually get the trailer weights off this one....
Good luck! By the way, the Dodge will probably be the only one in a half-ton that could pull a 5th wheel (and even then I don't know about that length...Plus Dodges are usually cheaper to purchase....
Oh and when you do decide to take the plunge, always look at least 150 miles outside of the D/FW area. It can save you thousands....