Cutting out

Does it cut out or miss above 4k? Or is it just right around a certain spot it does it then it clears up? If it's something like that it could be too much advance coming in too fast. So it only screws up in a small spot, then its fine at the higher RPMs.

I always double check fuel flow cause it can run great at low RPM then as soon as you push it, something like a clogged filter or screwed up pump will starve it very quickly. Where as usually with an electrical problem it will still have some sort of occasional miss at lower rpm. Although that isn't always true.

Had you taken it above 4k rpm before? Did it do it ok? If you have what have you replaced/changed since then?