Shaking/Shuddering while towing trailer

I have seen many people who had big problems trying to tow with small passenger vehicles. The factory specs say they can do it, and they can if you don't mind throwing lots of cash at things like transmissions and brakes. I have even seen vehicles where the doors would not close properly because the unibody construction had twisted/sagged. These vehicles are meant to tow a small utility trailer a few miles to the dump not to tow a full size TT and also load it full of people and luggage. And then try to climb a pass with the A/C on. The dealer will say it will do it and he knows tons of folks with the same combination because he wants the sale.