Chevrolet: lumina wont start after running for a while, chev lumina, sitting in the sun

Question
Hi there, I have a 1990 chev lumina euro. I am having trouble with it starting after its been running for a while or after it has been sitting in the sun, its like its too warm or something.  I know that sounds unbelieveable but its true.  If I drive it around for lets say 30 mins or so when its warm out the car just wont turn over altho I have a booster pack and it will start with a boost.  I have had the starter and the battery replaced. Any suggestions?

Answer
Deanna;
  Hi , I would check  the belts to see if it is loose or you can check to see what voltage it is putting out when running , if the voltage is too low it will not charge the battery. so see if you can have a volt meter put on it to check the charging volts.   ok