Ignition Coil Overheating?

[crm318]

I use my truck to do deliveries at my place of work and I drive it a good bit in a day (lots of starts also). Every once in a while, the truck will not start and just turn over. When this happened tonight, I had my timing light with me. I hooked it up and no flash. I poured a cup of water over the coil (HEI) and then sprayed a little carb cleaner to dry it off. It started right up. It happened again later on and this time, it wouldnt start. I had to let it sit for an hour. What could be causing this? How can I keep this thing cool? The coil is only a month old and the last coil did the same thing.