that is a REAL puzzler. do you have a stock dist of any kind that you could sub in for 1 day even tho the curve'd be way less than ideal? I'm trying to get a handle if it's fuel or ign & from the descrip it sounds fuel though an intermittent miss can be hard to detect (at high rpm) & sounds like you have a more than adequate fuel (supply) system. Vac adv on the MSD dist? (affects the phasing) EDIT are you checking the fuel psi at the offending rpm & past the filter right at the inlet? Mechanical pump also or just electric?