What gear ratio do you have on the Durango? Is it a factory tow package? That will make a big difference on how it goes. Years ago I towed a 18' 1600lb boat with a V-8 Durango and it really struggled on any hill. It was my first time towing anything and I didn't know anything about towing. All I knew was it had a good tow rating and was a V8 so it had to tow the boat alright! Well, I was seriously mistaken. Come to find out, it only had a 3:08 ratio geared for highway miles. After towing in the Sierras I Burned up the tyranny! Expensive lesson learned.