Rcimp,

Great work on taking the coil out of the equation. Choking off the air through the venturi forces the engine to pull more fuel through the carburetor. This is pretty simple mechanics....you indicate your truck starts and runs fine until warm, or about five miles. Using this fact one would look for something that is being affected by a warm condition that isn't present in the cold engine.

Any static condition in the carburetor, like a float that is set too low, won't change with engine temperature. Your thoughts on the choke and a vacuum leak or right on target...but this wouldn't be temperature sensitive.

Sort of thinking out loud, valves that are set way too tight will not seat properly after they warm up. This could cause a loss of vacuum which pulling the choke out would help.

If this problem is really brought on by a increase in engine temperature, and not by the 5 miles driven (fuel starvation), then it probably isn't the carburetor that is at fault.

Stuart