This is why I was wondering everyone's thoughts on it being lean, running very hot, and slight surge but only at about 2400. 4000 seems fine, but lots more fuel being dumped in too
Its possible to be too lean as one circuit tapers off and the other tapers in. Higher load reveals things that are covered with high gear ratios and high stall converters.
Even more common (too common) is too much advance between 1600 and 2800 rpm, even though its fine for the upper rpms.
I'm not saying either of these is the what you experienced, but they fit the symptoms.
