ECU issue

Check that you have good solid voltage to the system, IE 12-14 to the box, and "about" 10-12 to the coil with alternator running 14V

You've already "guessed" at two possibilities the pickup is certainly one. When I say "pickup" I mean EVERYTHING in that SYSTEM. The pickup, the pickup connector, the gap, dist. wear, debri and junk in the reluctor/ pickup, and the connector on the ECU and physically eyeball the pickkup/ reluctor for damage