Hello, thanks for requesting me.
If you were getting 114VAC @ 53-55 Hz, but are now getting 120VAC at 54-55Hz, there is a problem. If you adjusted the engine speed that much, the frequency should have really spiked.
There are 2 possibilities here.
1. You are using a digital meter. It is not very common with Onan, but sometimes you just have to resort to using an old analog meter. An analog meter does not show spikes. Even using a True RMS meter sometimes is not acceptable.
2. You may have a brush sticking in the holder. Although this most often would result in a higher frequency reading than what it is actually running, it is possible that you could get a lower reading. I have never seen this happen, though.
If the genset is actually shutting down before it gets up to 60 Hz, it is possible that the controller is bad. I have never heard of this happening, though.