We are generally waaayyy over the trucks GVWR. This is from experience towing a 35 foot three slide fifth wheel with a Chevy 2500. Most people in this situation advocate ignoring the GVWR and instead using the axle ratings. Since your truck has a gross combined of 19,000 pounds, I would suggest that you have two choices, one, is a newer truck with a higher gross combined ( current dodge is 23,000) or stick with a fiver of around 32 feet and no more than two slides and quit worrying about. From experience towing overloaded is not fun and I will never tell someone else to do it.
On edit, my current fiver has a GVWR of 14,500 pounds and scales about 14,000 when everything is said and done. This might be just slightly over for your current truck, but not much.
Don and Lorri
2007 Dodge 3500 dually