Mike,
I have a problem very similar to yours, but I've never thought about the tach being bad.
Mine feels like its missing right at the top of the gear changes (5800 w/ RPM activated air shifter) and sometimes in the speed traps (depends on track). I finally figured out it was the rev limiter kicking in for just a split second. I can pull the high side chip out of two step and the "miss" goes away. I was thinking it was in the distributor, but it could be my tach? My tach is a Autometer monster tach with shift light, about 21 years old. I will change it this week...
Brian