96 buick regal won't run

96 Buick Regal. Car runs perfect -----except when the under hood temperature is hot. Water temp normal. Car sitting in sun. try to start turns over perfect but no start. If it does start it is very rough like only hitting on 2 or 3 cylinders. Hear several very loud knocks ,like carbon buildup.(not pings) Don't try to move or it will die.Absolutely no power. Shift to nuetral or park and just set there. Might hear a few of those loud heay sounding knocks. Just wait and it will gradualy speed up the idle getting up to normal idle speed then you can drive away. Never dies after it smooths out. Now if it didn't start then try to start it about every 3 or 4 minutes and usually after about 10 minutes it starts and drives away perfect.
Could the engine be getting flooded when shut off and high underhood temp ? If so what can I do to correct the problem. Any other ideas as to what the problem is ?
Never a check engine light. Another problem may or may not be related. When cruising along if I give a little more gas to pass or to go up a slight incline in the road the car bucks until I let up on the gas.
Many thanks for any ideas. Everett

sounds like a fuel pressure problem to me. The system is vaporlocking, and doesn't have the pressure to overcome it.