first, your Astro was the only minivan to be a truly good tow vehicle.
with the 4.3 Vortec v-6 and that it was built on a ladder frame chassis, it had the highest towing capacity of all minivans and highly prized for that purpose.
second, the Highlander is a unibody construction and smaller v-6.
you're going from the Astro's towing capacity of 5500lbs. to only 3500lbs.
you'll probably get worse gas mileage when towing, not even factoring the strain you'll be putting on a far less capable tow vehicle.
third, i'll bet there's a frontal area limit to the Highlander, which your trailer will exceed.
fourth, the Highlander will only have a tongue capacity of 350lbs., which i'll also bet your trailer will exceed when loaded.
having the extra weight of the hybrid stuff, including batteries, will severely impact its payload capacity.
what does the car's driver door sticker say is the payload amount? don't rely on the internet or manuals.