I towed a small car 500 miles on a tow dolly last week. Got about 16 mpg thru hills, interstate and back roads. Plenty of power and no complaints. The whole set up was probably under 1800 lbs I'd guess. My Sprinter basically did the same with the same rig.
I found it towed better and the mileage went up if I didn't put it in the Tow Mode!