Are you using a DECELSTOP command in your G0 logic? When running in Singlestep mode, I suppose that the Camsoft adds this command in the background, because it knows that your motors must come to a decelerated stop between every command.
In Auto mode, you need to tell it to do this. So insert that command in your G0 logic and try it again. If you are working at extreme feedrates, you may also need the command in your G1 logic.
This will make a jerky machine motion though, if you are running short segment toolpaths. So that is when you would call for the SMOOTH ON and SMOOTH OFF commands, in conjunction with the G1 logic. These commands need to be issued at the beginning and end of each chain of G1 movements. I'm not sure what will happen if you try running with SMOOTH ON through a G0 movement. Likely not good
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)