I believe you can be found negligent, and therefore liable for damage your rig causes if you are towing in excess of your tow rating, by any decent ambulance chaser. The negligence is the act of towing in excess of your rating.
What "tow rating" are you writing about?
If you are referring to the manufacturer's GCWR ie gross combined weight rating or the manufacturer's maximum trailer tow rate you are unfortunately misinformed. Is is just not true.
Nobody gives a hoot about that rating and few ever heard of it. The only place where those numbers ever show up are in the marketing hype in the sales brochures. DOT officers DO NOT have this info and don't care about it.
When the RV industry was busy a couple of years ago there were literally several thousand of us RV transporters covering the highways of 48 states, sometimes 49 states, and most of the Canadian provinces on any given day of the year often towing heavy trailers.
One of the largest, most prominent, and most professionally run transport companies in the industry was (is) Horizon Transport of Wakarusa, IN. They hire full-time compliance guys who closely monitored everything we did. One of their first requirements was that our trucks, ordinary dually pickups in most cases, had to be registered for 26,000 lbs. Mine was and so was my '06. I was inspected by DOT officers on numerouis occasions and except for one "no log book" issue (another story) I was always completely in compliance.
Federal and state DOT officers consider whatever weight the truck is registered for as the legitimate maximum weight AS LONG AS the tow vehicle does not exceed it's GVWR or GAWRs.
There are hundreds of hotshotters pulling heavy tandem dually gooseneck flatbeds hauling general commodities or, like member EB, oilfield components. Their trucks are legally registered for 30,000, even 40,000 lbs. and they are required to cross every scale they encounter.
There is simply no truth whatsoever to the internet myths that are spoken as gosple every day regarding factory combined weight ratings and threats that your insurance company will drop you if you have an accident and are overweight. Insurance companies are regulated by state governments and generally speaking are not allowed to drop their insured until after the claims are settled unless, possibly, the insured has provided false information to the insuror or is in violation of policy restrictions.
I have a CDL A which allows me to pull any combination vehicle I can tow as long as I don't exceed my truck's GVWR or GAWRs. I have crossed scales at gross weights in the 25xxx lb. range and once was waived through a Kansas scale pulling a very large, very heavy, Alfa Gold that was owned by an elderly retired couple and contained everthing they owned. I was probably at 29,000 to 30,000 lbs. It was legal because the trailer was registered and had it's own license plate so I could exceed my own registered weight of 26,000 lbs.