Our 6 cyl 2006 4 Runner with factory tow package is rated at 5000 lbs. Our Lance 1685 is pushing the limits at 3600 dry weight, we figure about 5000 loaded.
Here's a post I wrote about the pros and cons after 10,000 miles:
Towing a Travel Trailer with a 6 Cylinder Toyota 4 Runner Ideal? No. Safe? We haven't had trouble. We know conventional travel wisdom says not a good idea. But my husband said I could have a travel trailer, but not a new truck, so I had to find a trailer our 4 Runner could tow. One of these days we'll get a new truck and it'll have more margin for error in tow capacity.