Electrical problem or something else??

My car will start fine and run. However after I get to my destination, and shut it down, I won't be able to start it again for anywhere from 5 to 20 minutes. This is particularly aggravating when I pull up to the gas pump, get gas and then my car won't start again for a while. When it finally starts, it seems to run fine. This isn't an intermittent problem. It does this EVERY time. I have replaced the TFI module, plugs, wires, fuel pump, pump relay, the cap and rotor are not old at all and appear to be just fine. When it doesn't start, I have spark and fuel. The motor just turns over but doesn't fire up. It seems that something is heating up, and has to cool down before it will work again, but I don't know what it could be. Any ideas?