I tow a 2720SL with a 2006 Sienna. I know that I'm not the only one to do it; there used to be a SiennaChat forum, and there was a member there who did the same, for many, many years, without issue.
That being said, I do have two huge caveat/YMMVs: #1, I have not yet weighed the set-up to see if or how far out of spec I am. That's on the to-do list this year. #2, I live in the Midwest, where the terrain is low and flat. I can get away with a lot more than those who live/travel to the mountains, for example.
Towing a TM which is low and minimizes sway will obviously be a better situation than towing an upright of the same or less weight. And yet, the weight ratings don't take any of that into account. For that reason, I do feel safe towing a TM at the "limit", as it were. This is a matter of some discussion and debate, and obviously each person must make up their own mind as to what is safe and what isn't. I personally refuse to believe that 3500# is some magic number above which everything goes splat. There is overengineering, legal considerations, marketing, etc. that goes into these decisions as much as the actual capacities of the vehicles.
One person's opinion...
