471 Big Block high rpm problems

That makes sense... I listened to your video, and when you rev'd it once and then rev'd again immediately, it broke up, which sounded like an accelerator pump issue.

By the way, the engine will not behave the same when running under load on the highway at speed as when you are revving it in neutral. There is no load on the engine when sitting still, and the fuel-air mix in the cylinders will not be the same as at the same RPM's when running under load. As the air-fuel mix changes with load, the spark energy and voltage required to properly fire the cylinders will change with RPM's.

Do you now have an AFR meter, with the oxygen sensor installed in the exhaust pipe behind the engine?

What are your full cam specifications? I ask because that vacuum level that you show on the gauge at 850 RPM in gear could be too low.