Have watched  your Youtube documentaries for a few years now and learned many, many things.

My 2000 GMC C3500 Dually has 165,000 miles and is an automatic with a 454 Cubic In. gas engine.  The issue is this; it will start up immediately every morning but once i operate it for about 20 minutes, park it for 30 minutes and attempt to restart it, it turns for a little while before starting.  if i let it sit for 45 minutes, it turns over for a longer period of time before starting.  if it sits for an hour, it takes even longer to start, and so on and so on until it turns for so long that i have to stop and retry 2-3 times until it finally drags itself to a start.  Diagnosis indicates #1-good fuel pressure and volume. #2-fuel IS getting to the cylinders.  #3-Main Computer is not telling the cylinder to fire until a few rotations have occurred.

I replaced the Distributor, the Cap, the MAF Sensor, but I nor my mechanic of 30 years can determine what else could be telling the main computer NOT to fire after the truck has run for a little while and sat for different periods of time.  But yet every morning it starts up better than a brand new vehicle??!!

My mechanic does not want to just replace the main computer, thinking it may be the main computer that is going bad, but would rather replace or fix what is causing the main computer to do what it is doing.  I figured by replacing the MAF sensor, this would have corrected the issue, but it did not (even though it did help that problem about 50% and made it run much better).  

Do you think that i should just go ahead and replace the main computer or is there other sensors that would cause the main computer to do what it is doing?  Before I burn my starter, I figured I would present the problem to you for a final opinion.

Thanks and hope to hear from you.  

JCL