Check the European towing specs for such vehicle. The US towing ratings are a combination of the mechanical capabilities of a vehicle in conjunction with the handling and braking abilities at Interstate speed limits. In European countries where towing speeds are limited to approximately 55 MPH the tow ratings for the same vehicles are generally higher than in the US. There are of course exceptions where vehicles are rated in Europe the same as in the US. Gone are the days where you could add a hitch to the family sedan and tow 5,000 lbs. ; the automobile manufacturers have now created the need for us to purchase a truck to fulfill those tasks. Accordingly they bump up the towing abilities of trucks while minimizing those of family vehicles. The Federal Government does not assign the tow ratings, it is the automobile manufacturers that do; so while it might be legal to tow in excess of the ratings the Insurance companies are quick to stand by them limits. The fact that other vehicles with the same engine and transmission are rated to tow 6000 lbs. does not mean much; if they have a heftier suspension, more rigid chassis and heavier weight may easily explain the added capabilities. The fact that you have towed the higher load for 10,000 miles with no negative effects speak for itself. If it adequately handles the terrain in your area and your towing speeds are reasonable then your vehicle is adequate, just don't get into an accident. Or you could purchase a $40,000 dollar truck to tow your $15,000 boat.