I have had a bad tach cause a car to miss above 3000 RPM Any elecrical component on the car hook to the ignition can and (if it is me ) will cause problems try doing the process of eleiminatios as already suggested, remove one component at a time, tach first, shift light and so on. I have also seen MSD chips go bad and cause a mis at a lower RPM than written on the chip Good luck, let us know what you find and the cause