I've had two instances where it was difficult to start my blazer.

The first was after towing on a 90 degree day 150 miles at highway speeds. After I parked it and took the trailer off I got back in to start and it would fire. After several attempts the negative on the battery fell off. I put that back on and it fired up right away.

Fast forward two weeks to today and I couldn't get it started. It was around noon and another hot day. 24 hours before it was running fine in the heat. This time there was no battery cable problem. I tried again a little while ago since it is quite a bit cooler and it started right up. I drove it around to operating temperatures and it was fine to start again.

It seems like a vapor lock happening or is it a more serious problem?

 

Meaning, I assume, it wouldnt crank. Not related, IMO. OR it did crank alright until the cable fell off.. ?
If the engine was at air temperature and it wouldnt start, probably not vapor lock. That would manifest when starting an already warm engine... though it would still be a good idea to get a fuel pressure gauge and check the leakdown rate.

pressure > 55lb, over 50 for ten minutes IIRC

 

The first instance it would crank but not fire until the cable fell off. Then I put the cable back on and it fired right away.

 

Well it happened again. Would not fire up. I tried for about 30 minutes and decided to put fuel down the intake and it started right up and drove 40 miles right to the mechanic with no problem. I don't have the time to work on it the next few weeks so I will let him deal with it. I'll let you know what he finds out when he digs into it tomorrow.