My 400 cu.in with a Edelbrock Performer intake and 750 cfm Holley tends to act like its vapor locking after it runs warm for about 20 minutes.  While running it seems to perform fine but when the RPM drops to in-gear idle it wants to die.  When I try to restart it, it acts like its flooded. It will finally restart but not without a bit of cranking.  

Any ideas anyone?  

Check and make sure your fuel lines aren't running too close to the exhaust or engine block. Too much heat near the fuel lines will cause vapor lock.