You can tow up to the limit, but you may not want to. Like others have said, payload is many times the limiting factor.
Just because you can pull a load may not mean you want to. I don't like working a machine at it's max, I like to have a little cushion. Also like others mentioned, the terrain plays a big part of it. I'm towing at 80-85% of my max, and the truck does fine going to the beach, but this past weekend going up a really steep hill, I got down to 24mph, and that was all she would do in 1st gear.
If you plan on towing any in mountains I would stay under around 80%