My car has been running the best it has ever ran, yesterday i came off the highway and at the stop sign it started missing real bad,even choked off and stoped. I started it up again and still a bad miss. It only misses at ideal and low rpms, under 3000. At higher rpms it runs great. Its a 468 big block, Holley HP ,barry grant preped, carb, locked out HEI with MSD digital 6 box. Can't seem to find the miss. need some help