Please help fast!! No start when hot

I have a 1991 bonneville 3.8 that is acting up. When the engine warms up, and you cut the car off, you cant restart it right away. You have to sit there and wait for it to cool. If the engine is cool, it will start every time. I have replaced the coil several times, the coil module, and the computer. This is getting more expensive than the car is worth but we really need it. help!