Earlier this summer I towed my wife's Acura TL from Memphis,TN to Beaumont, TX. I rented a car trailer from U-haul. Total trip was about 600 miles. The trailer weighs about 1800 lbs and the car is about 3800 lbs. Over 5500 lbs total. I did all interstate driving and at 70-75 mph I averaged 12 mpg. I was impressed because I pulled a mustang once on the same type of U-haul trailer with a 350 1 ton Chevy it wouldn't go any faster than 65 mph.
The factory programming really is tuned for towing performance. My truck has the towing package so I guess that helps. All in all I was impressed and can't wait to tow again with the truck.
Below is a pic of the truck and her car.