I have a travel trailer trailer with GVWR of 5,300 lbs. The most I think the trailer weight will be is 6,500 lbs. I have a 2014 Durango with a hemi, trannie cooler including heavy engine cooling. My concern is 3.09 differential. Of course when towing I will take it out of econo mode. What does econo mode do? Does it change the differential from 3.09 to 3.45 or does it basically take it out of over drive. The manual does state my Durango is rated to pull 7,500 lbs.