Still have the problem. At ~4500RPM, engine starts cutting out, tach starts bouncing (not all the way to zero)... letting off slightly it smooths out until about 5K RPM.

More investigation reveals that the problem manifests itself regardless of load or gear - it will do it in first, second, third - even in park, whether you floor it or let it creep up under light throttle. I no longer suspect fuel... as much.

I did the static checks of the RPM sensor for continuity - reads right on OEM spec. Resoldered the fuel pump relay just for thoroughness. Since it does it in park, I put a timing light on it to watch what happens - timing seems to stay more or less on target for the first few misses, then I see it getting pulled back.

I'm running out of ideas on this one - it seems to be spark related, but tied only to engine speed - could it be the RPM sensor? Or is my coil the prime suspect? Thanks for any guidance...