I tow my 37' R-Vision Toy Hauler with my 2005 2500. I took it to the scale once it was loaded with everything but food and my Harley Trike. I had less than 5,100 pounds on my drive wheels. I do not remember what I grossed out at but it was right around 22,000 pounds, which would put to Toy Hauler at approx 14,400 pounds as the truck is right at 7,600 pounds when ready to tow.
My Truck has done fine and I have towed as much as 500 miles in one day. The only mountains (or Hills to some) were in Northern Georgia and it did fine running in Tow Haul in OD with the cruise control set at 63-65 mph.
Would I rather have a Dually, you bet but my truck is fine for now. It has Air Bags Plus Helper Springs and the tires and rims are good for at least 3,700 pounds each.
Before any of the WP jump in, my DW is a Insurance Agent for many years and I am covered.