I towed a 6,000 lb. trailer for 9 years with a Dodge 3/4 ton window van, and in certain respects I liked it more than our current TV. It was the 5.9L with 4.10 rear axle. Loaded and ready to camp we were about 1,000 lbs. below our GCWR and I don't know that I would have wanted to to get any closer to the maximum. Performance was adequate for all but the longest and steepest grades.
Both the previous replies you your post are right on the money. I flirted with the idea of getting a Ford E-350 diesel van for a while, but I couldn't justify the expense as it would have been my daily driver more than anything else.