If it’s truly rpm related(doesn’t want to go past a certain rpm under any condition), it’s likely ignition or valvetrain.
If it’s load related, it’s probably fuel.
My test for the fuel would be to run it at wot thru the gears, but shift at an rpm lower than the rpm where you normally see the problem.
If you can start in low, go thru the gears and make it well into high gear at wot without it nosing over....... it’s probably not a fuel supply issue.
Another rpm related test is, go along in low gear at a light throttle setting and crowd the rpm where the problem occurrs.
Lightly crowd the throttle to get to the rpm point where the problem occurs.
If it runs clean right up to just under a certain rpm, and seems to be like there is a rev limiter...... then I’d look more at ignition.
If you’ve ruled everything in the ignition out, then look at the valvetrain.
I can tell you this, on the dyno...... it isn’t that unusual to see a valvetrain issue show up very predictably at the point where things get unhappy.
Just like flipping a switch.