Dennis, I found two new references to higher tow capacity; 7,100 pounds for V6 and 7,900 pounds for diesel.
As you suggest, they seem to be based on GCWR of each minus lightest van minus driver. I assume the 800 pound difference is due to diesel having 1,000 pound higher GCWR but adjusted for diesel van being 200 pounds heavier.
My concern is about how they would attach a Class IV receiver to a lightweight unitized van body. Are the frame rails that strong? Mercedes Sprinter has tow rating up to 7,500 pounds on some models, so structurally it's possible. I just don't want to depend on inconsistent data when most states max towing is 5,100 pounds. RAM needs to clear this up.