Hi,
The available resolution depends on the actual PWM frequency, you can see in the code how Bruce has calculated it for you. If you haven't changed the code the resolution is 10 bits (0-1023).

The PCPWM module have a configurable dead-time generator which inserts a deadtime between turning off the upper switch and turning on the lower switch. When aproaching the "ends" of the available resolution this can distort the output waveform and I suspect that is what you're seeing.

If you don't need deadtime you can turn it off. If you do need deadtime you should make sure that the dutycyle never aproaches the values where you're starting to see distortion. You usually can't use extreme dutycycles anyway due to the MOSFET/IGBT highside drivers need to refresh its bootstrap capacitor charge.