A complete tuneup would definitely be in order if the state of tune or when the engine was last tuned up is unknown. While the plugs are out, I'd also suggest a compression test on the cylinders and then performing a vacuum reading with the engine running. Short term, you could unhook the vacuum advance and re-rev the engine back up and see if the sputter is still there. If the hi speed miss reduces or goes away, then you've likely just got too much ignition timing for a 'no-load' situation; to a small degree, this will be normal if the vacuum advance is working correctly.
If the vacuum advance to the distributor is hooked up to 'direct' vacuum instead of 'ported' vacuum, then you can potentially have too much ignition advance. There's also a chance the initial ignition timing is just too high which is promoting the hi-speed miss. I'd suggest using a timing light on the engine and verify where the intial timing is residing and observing the timing readings while varying the rpms with the vacuum line both hooked up and unhooked to the distributor. And I have to ask if the same miss is apparent when driving the vehicle or just when speeding the engine up in neutral.
And of course the last scenario which falls back to your previous post, if this is a Load-O-Matic distributor hooked up to a late model carburetor, then you can potentially have too much advance under a part throttle or high vacuum situation depending upon if it's hooked up to a 'direct' or 'ported' vacuum source.
Lorena, Texas (South of Waco)