I tow a 30 travel trailer. 9950 lbs with full tanks and our camping equipment on board. XD toes it like a champ. Your mileage will suffer much more from a load with a lot of drag than from a lot of weight. I have also towed a flat deck trailer with steel plates as a load. Just over 10k total weight at the time. Still got 17 mpg on the highway at 65. I really want to get a 5th wheel that is around 12k actual weight with around 2k tongue weight. Really want to see how it handles at its "max".