We put over 100,000 miles on our 2001 V10 pulling either a Buick on a dolly or a Jeep wrangler 4 down. It's been in and out of Skagway Alaska (12% grade for 12 miles) and through the Eisenhower/Johnson tunnels half a dozen times. The only time it lacked for power was when the fuel filter got plugged.
We have over 16,000 miles on our 2013 V10. It also has been to Alaska, Florida, and all points between pulling the same Jeep. The mileage for both has been a little over 8 mpg when towing.