I didn't see mention of what kind of carburetors you are running. Does the mini-HEI have an external coil, and does it use a vacuum operated advance.
Have you put a timing light on the engine and checked to see what the marks do when you pop the throttle a bit...do they move around as they should.
If the truck actually gets harder to start as it warms up, the problem is obviously tied to temperature.
Tight valves could do this, as well as an electrical/electronic failure.
Does the HEI require a full 12 volts at all times.
Sorry to answer your questions with my questions!
Stuart
