Maint Display 12 Low

[Radman]

2001 GTX DI has long beep maint display as well as 12V Low. Cannot get above 4500 rpm on the lake. Starts to misfire. Installed new battery, checked voltage before starting and at idle. Shows around 12.5 volts. When I rev to 3000 rpm the voltage does not go to 14V. Swapped out the rectifier from sister machine, same model year etc. Same problem. I suspect it has to be a stator. Can I swap the stator without having special tools to test or is there a way to test stator without removing? Thanks Radman