I have 1977 el Camino with a 400 sbc. All cylinders have 120 plus compression.Hyd valves adjusted. HEI ignition, new rotor,cap,coil,wires,plugs.New carb. No vacuum leaks at all,When I pull each wire one at a time I get the cylinder drop off as expected.All wiring has been checked.The miss like I said is random not evenly spaced like one particular cylinder is not firing. I am at a total loss as what to check next,any ideas?