Rewatching a couple times (for fun), that black poot could be once the secondaries open theyre too rich. That's my guess. That pull was to 5k (best power) and the previous test run he said the air doors didnt open till 4300rpm, so there may be something to that.
your secondaries are mechanical and were open long before that point... if the air valves don't open when the secondaries do the car bogs......