Ignition wiring from ignition switch thru connector thru bulkhead thru to coil. Make certain that is wired to positive side of coil. Check entire path with meter or test light while helper wiggles entire path of circuit. Basically ensuring that you are receiving proper consistent voltage to coil.

Feel any miss at higher rpm or during acceleration under load? Sounds like not doing well there either.

Try running a wire directly from battery to positive on coil as a short cut.