I'll be the guy who just says it. I did take Teton Pass from Jackson over to West Yellowstone in the summer and didn't think it was a big deal. My loaded TT (30' point to bumper) is around 9,000 lbs and it is towed with a modern 1-ton diesel truck. However, I do tow frequently in the mountains and feel very comfortable doing so. My TT has very good brakes which were redone about two years before our Yellowstone trip. I had no concerns or problems towing Teton Pass.
You have a very modern truck (the diesel on order) and engine brake so personally, I would not think twice about pulling your combo over Teton Pass given summer conditions. I would not consider it if temps could reach or were just in freezing conditions.