We try not to suggest shotgunning 3 coils as a troubleshooting step. If a misfire is suspected, swapping coils around, or swapping in one new coil in each location is a much better alternative.
With ignition problems, checking the primary and secondary coil resistances is something easy to do, as is checking resistance of plug wires and inspecting plugs.
Fueling is rarely the issue with these types of problems. Over 95% are ignition related.
Low alternator output can indeed cause low spark voltage.