Pertronix failure modes -- high RPM issues?

[ChickenPinz]

For a long time at higher RPMs (>3,000) my tach (Sun Super Tach II) sometimes bounces around a lot, but it's super stable at lower RPMs. I've largely dismissed it as a tach issue, but today I noticed a cutting out of engine power on the highway and the bouncing needle was more dramatic so the issue seems to be real.

Are there any known failures of the Pertronix setup (with original cap) that show these symptoms?

Just looking to leverage the wisdom of those who've gone before me before digging into the wires/distributor/coil.