Dirt or asphalt? In dirt the tires will be a big factor. On the pavement, the truck with the heavier weight will have the edge, provided it doesn't break traction. I assume you will have them in low range. The posi should help the durango, and I think it probably has an edge in the weight department. What about rear end gears?
My 4.7 Dakota had no problem towing a uhaul w/ Ranger through the hills of WV @ 65 mph+.
Too many variables to get a definate answer...but I would give the nod to the Durango.
Let us know how it turns out.
