The factory considers possible warranty claims while determining towing ratings. If they didn't, on older trucks, a 460 gas (Ford as example) would have the same rating as the diesel as all suspension, brakes, tires etc. are identical and the power is similar. It is 2000lbs less. However,the 460 will carry more than a diesel as the gvw is the same and the gas engine is lighter. Here in British Columbia, the factory rated tow capacity (gross combined) is the law. Just ask all the U.S. visitors who got charged while towing big fifths. They won't let you move it at more than 10% overloaded. Your problem, they don't care. You might not get stopped, but don't get into an accident where the police or our government insurance is involved.