New engine gremlins - frustrating

Just some random thoughts FWIW:
- I have to wonder if everything was well warmed up in only 5 miles.
- IMHO, tuning out this relatively small symptom would be down on the list until there was several hundred miles on the engine.
- With the center hung floats, the corners should have less/no effect on fuel level in the carb bowls, but speeding up/down may effect it.
- Does this have an Air Gap intake? Not the best for a cool engine in cold temps.....
- Consider putting a vacuum gauge on the engine and watch it to see what the vacuum levels are when this happens; it may give you an idea of what carb operation is in play when it happens. For example, it may tell you that the vacuum is dropping to where the vacuum secondaries are wanting to blip open for a moment; it would only take a hair of secondary opening to lean things out.