Why does my mustang 5.0 bucks when it gwets hot?

If "hot" means higher than normal engine temperature, the fuel in the fuel rails may be boiling due to heat radiated from the hot engine below. The engine will run rough and starve for fuel if there are vapor bubbles since the fuel injectors are designed to inject liquid rather than vapor. If boiling fuel is causing the bucking condition, pull over and open the fuel tank cap carefully. If the tank is highly pressurized, then boiling fuel is causing the problem. Keeping half a tank of gas or more will minimize a boiling fuel issue. Driving on a nearly empty tank will make a hot fuel issue worse. If the engine is overheating, repairing it to run normally will keep the fuel from becoming overheated too.