Highlander has 16.5:1 1st gear plus diff in high range. 4Runner is only about 13:1. Highlander has lower gearing and more power. For a single to trip - might actually tow better.
Food for thought #2
Highlander Hybrid has about 100 more hp and more torque than any 1990 F250 with any available engine including the 460 or the diesel. Highlander also has larger brakes than a 1990 F250 with any available option.
My buddy tows his boat and picked up a Nissan Armada. 8,500 lbs. towing capacity. He is very happy. FWIW, he has a 4th Gen 4runner and will not tow with it though his boat is well under 5,000 lbs with his trailer. It is just too close for comfort.