I tow 21' Sea Ray and a car trailer, usually with track car on it, with my '12 35D. As a matter of fact I bought it because of the boat. The previous '03 4.6is was doing a brilliant job even with 7k lbs car trailer, but the boat was just too much for it. Diesel, on the other side, is made for this job. When in auto mode in a regular traffic it will hold the gears for too long and i shift it manually, but this is the only complain that i have. On a flat terrain and ~65 mph I can get 15-16 mpg with the boat and up to 19 with the car trailer. And of course i feel angry that BMW omitted the 8 speed tranny from the diesel, it could have been the perfect SUV ever. I am also missing the rear air suspension, but that will be corrected soon.