Toyota Sienna as tow vehicle?

If the Sienna has the optional tow package, it's rated for 3500#.

I thought the "s" in 320s meant shower.
We're happy using our 2005 Sienna, and we were told that it came with "tow package" which only meant a change to the cooling system, but we still had to have a hitch installed to pull a small utility trailer.  That only needed wiring for a 4-wire connectorn but when we got our T@B, we had to have it rewired for 7-way connector, plus a brake controller & hot lead, which all came to over $500.

Thanks, @rajamar, for the tip on the AirLift 1000 bags.  We have always known that our aftermarket tow bar (not an option from Toyota apparently) fits rather low, but the Sienna's softer springs that give it a car-like ride also make it sag a bit while towing large loads.  While not a major issue, we occasionally drag the bottom of our hitch (tightener bolts hang down) when going in/out of some driveways or gas stations. 

So, I finally got around to looking into them, and all the positive reviews convinced me to give them a shot.  A number of reviewers said it was an easy install, and I still had the old "creeper" & ramps, so yesterday I managed to install them myself..

The red cylinder above is one of the Air Lift "bags".

Ideally, a mechanic would put the car on a hydraulic lift, but I used ramps to make more space under the car, then used a Jack in the center to raise the car, which extends the coil springs to create more space between coils for inserting the deflated air bags.  Wheels were never off the ramps though.

More space between coils makes a huge difference when it comes to not only inserting the bags, but also for connecting the air tubing to the bags.  There's not a lot of working space, so for someone like me  without much experience working on cars, this can take a while, like most of the day in my case.  Some essential parts are not included in the kit, like cable hangers for mounting the hose in some places, hex screws (1/2" #10 self-tapping), and 3/8" split loom, and an extra long drill bit in one spot.

Here's what my installed air bag looks like.  I used the prevailing recommended method of installing with the tubing connection at the top (contrary to the written instructions) to avoid having it close to the ground.  To avoid leaving the bottom of the bag in direct contact with metal edges of the bottom moving end of the spring mounting, I inserted a disk of 1/4" non-compressible rubber under the bag.

I installed the air valve for pressurizing the bags in the back corner just above the hatch holding the jack, since there's access from underneath through a rubber grommet inside that compartment.  The most time consuming part is running & mounting the air hoses.  I used the method shown in detail in this video..
https://youtu.be/EF4UALNJcw0
I test drove the car without trailer, with bags inflated to 20psi, and I did notice better stability on turns, with less tilting.  Will look forward to testing at 35psi with trailer to see how much difference it makes.  I'm thinking it could also make a difference in being able to switch from jack plate to wheels on the jack, which at times can be difficult due to the sag in the rear end.
PS:
At 24 hours after test driving, pressure is holding, so no leaks!

As a new 2022 Tab 320 owner, I just towed with a 2011 Toyota Sienna.  Round trip about 4000 miles.  Seemed pretty good, no issues with power going through the Appalachians.  Instead of Airlifts, I had Timbrens installed to help with the squat and improve handling.