Can anyone help with ArtCAM (2017 pro to be specific)

I followed a ArtCAM video and created a plaque. according to the simulations everything I did was proper.
I created a machine relief toolpath and during the roughing stage portions of the castle and Dragons body were cleared away. (but I left teh roughing finish.

During Finishing there were 3 or 4 passes were about 4 mm lower that it should have been.

Q: is generic Gcode same as GRBL? and what is the difference between g Code vs G code Arcs?

Looking of the internet I someone suggest Mach 3 for GRBL on an arduino UNO.
What are the differences between all these choices?