BTW -

Check that your cylinder baffling system is complete, tight to the
cylinders and properly secured to the engine, and that air loads don't
cause it to deflect away from the fins. You seem to have had a lot of
cylinder agony.

Do you have a balance problem? Above 1700 RPM the engine mounts may be
able to isolate a still-running-rough engine from the cockpit.

Be sure the plug gaps are small enough that you don't cause a marginal
ignition harness to flashover at higher power.

Does carb heat smooth things out? If so the engine is running lean.

It could also be an intake manifold gasket that has sucked in, except
that I wouldn't expect the idle to be smooth.

NRPetersen