I have a 1964 327 ith a 1977 HEI distributor. replaced. Cap and rotor it Idles GREAT but when it hits 2000rpm it runs extremely rough.
May want to get the coil checked. Could be your loosing spark. Make sure the spark plug wires are good. Double check the firing order also.
firing order is correct the coil is less than a year old.
Maybe its running out of fuel. Another thing is there an EGR Valve on there and working properly? If it is stuck open a bit, makes it want to cut the engine out .
Looking for a Used Chevrolet in your area?
CarGurus has 44,107 nationwide Chevrolet listings starting at $1,500.
Search Chevrolet Questions