Our 2002 Toyota Highlander has horrible traction in wet weather, despite the highest rating (A) tires. Is there an aftermarket skid control package that you can purchase?
Does it still have the original Goodyear Integrity tires on it? These tires are terrible in the rain. I replaced mine with Yokohama Geolander G-051 tires and it made a huge difference. It is better in the wet and dry.