Effect of tow vehicle weight change on towing capacity

Never have paid much attention to cars. But trucks, GVWR + Advertized tow rating *when properly equipped, was more than the GCVWR. And to be "properly equipped" you had to have all the power and stopping stuff, but you had to move the seat, run down the windows your self.
Maybe if you strip out all the extra seats, carpets, and the FREDs you might get right.