Don’t want to be a naysayer but a 4Runner is rated for 5k pounds, deducting for what else you have in the car.
Towing overweight is extremely dangerous because you may not be able to stop. The transmission and driveline issues are a money issue, but not being able to stop, or loss of control generally, gets people injured and or killed.
Moreover, if you get into an accident, and you are overweight, it is likely you or your insurer will bear significant liability. And the liability could exceed your policy limits.
If you want to tow a track car, a horse or a boat of any substantial weight, you need to have at least a half ton pickup fitted properly. Our half ton is rated for over 11k pounds, which means you can tow an open car trailer with a car, a horse in a horse trailer, or a good size boat. Having towed a car and a horse, with proper trailer brakes and the factory controller, the truck handles it fine. We also have a 4Runner and you couldn’t pay me to tow any of those things with it, certainly not for any distance. And I love the 4Runner but this is not what it is built for.
In terms of risk, people should realize that let’s say you an undertake an action that 9 times out of 10, or even 99 times out of a 100, is beneficial, but the one time it isn’t you could be seriously injured or die - that is not a risk that a prudent person takes.
I realize as I type this I sound like my dad, but the reality is that factory tow ratings are not optional guidance but something that should be followed strictly. Besides injuring yourself, you could injure or kill others. Not worth playing around with. If you have only occasional need to tow, rent a 3/4 ton diesel pick up. Get one of those, be smart, and stay safe.