Had something similar to this, the difference being that at about 5k the motor would just about nearly back down to idle RPM (this was at the track, so literally 2 secs after shifting to 2nd gear). As it turned out my fuel system was the problem, or specifically the filter I had placed in front of the Carter mechanical fuel pump.

It worked fine having been installed that way for about 3 seasons, this was NOT the correct installation though. The minute I removed that filter I had my fuel pressure back up and no issues.

I suspect that in my case maybe the pump diaphram just wore down enough that it could no longer overcome the pressure obstruction in the line which the filter element presented.

Anyways, it was weird, work the day before just fine, then all of a sudden it "gave up the ghost"...LOL!