I read an article in Trailer Life magazine maybe 15 years ago, that said if you are involved in an accident with a trailer being towed behind your vehicle, and should be accident appear to be the fault of another driver:
If the other driver's insurance company would have your truck and trailer weighed, and the weight was over the GCWR the maker of your truck recommended, you could be held partially at fault for the accident because you were negligent. At the time I read that article, I was towing a 6400 lb. loaded travel trailer, with a 5000 lb. pickup. My truck was rated at 5000 lbs. towing capacity with the 4.9 six and the 3.08 gears, with a total GCWR of 10,000 pounds. So I was 1.400 lbs. over the factory GCWR. Did it worry me...yes, a little. The same model F 150 with the 351 V8 and a 3.55 axle had the same suspension and brakes my six-cylinder model did, yet the tow rating was 7,900 pounds with a GCWR of 12,500 lbs. Sure, it could pull the 6400 pounds better, but stop and turn better? Nope.
I think back to that article sometimes and wonder if the author was just trying to worry readers needlessly.