Alternator voltage output.

[kou]

Having a slight issue when driving and has been happening for a long time. Between gear changes I notice my headlights dim a little then go back to how they were I also notice that my gauges that I have installed also look a little dim. This problem happens about 90% of the time after starting the car and continues the other 10% the lights are always bright and my gauge lights are bright. Battery is new voltage when car is running 13.8 when I put loads on high beams and blower motor on high voltage jumps to 14v then drops to 13.4 then back to 13.8 or a little lower.not sure if I should but a new regulator and brushes in the alternator. Any help would be appreciated.