Dave,
You did not say what year your Durango was, but I have a 1998 5.9V8 with the towing package. I ordered it new, and it does a great job pulling our 2002 3326 King. Just as an ounce of prevention, you might want to make sure you have a transmission cooler to prevent damage. Also, make sure you do not tow with overdrive on. Make sure you push the button to lock out the overdrive. A lot more torque!!. Also, towing in overdrive can really damage the torque converter.
Hope the info helps. I wouldn't want a fellow TM owner have problems down the road.
If you have any questions, just let me know. Would be more than happy to answer any questions.
One other thing, I bought a sway bar for the wieght distribution hitch. Made a world of difference, and gave me piece of mind and safety for the family.
Bob Strong