Volts??? How many volts should I have??

It may be your volt meter. I would guess with all those new parts everything is just fine. Mine is around 14.5 volts while running.

As for the engine seem slower, hmm. Hard to think changing the coil would make much difference. Maybe the spark was weak and now with a stronger spark the fuel ratio is a bit lean. Always best to jet up and down to see were the best power is.

If your plug wires are old, you may have damage the coil wire changing the coil.