HEI acting like a rev limiter w/ video

First, put a timing lit on there, and look for the dropped sparks and watch the advance, to see what it's doing.If the advance is steady and around 20 degrees or more, and the strobing is normal, then
second;
it could be a fuel problem. 2000rpm is still on the transfers but about to transition to the mains. If you have a metering rod carb, then I'd provide some enrichment first and see what happens.
If a Holley, first I's stick a 10.5PV in there and second I'd go up one primary jet size, and again see what happens.
If you think it's going lean, the easy test is to wad up a shoprag and start covering the primaries with it, while it's in stutter-mode. If it smooths out and starts acting normal; badaboom.