My dad had a 1975 240D (manual transmission) that he bought new, and he towed a little trailer with it. Probably the total weight of the trailer was under 2000 lbs, but it worked.
Didn't go up hills so fast, though.
If I were doing this with an automagic transmission, I'd definity add an extra tranny fluid cooler. Otherwise the tranny would probably burn up and die.