NO, I hadn't! I remember adjusting that years ago, but in this recent episode I had not touched it. I just checked and it was set to 0.001!
I just googled it, as frankly I forgot what "Shuttle Wheel" settings do (yay for archaic names) and apparently that is tied directly to backlash acceleration rates... Boy am I glad you asked me this. Apparently on servo systems they tend to run terrifically small numbers for this, but on stepper systems it should be quite a bit higher.
I just adjusted it to 0.050 and it does make a pronounced difference. The odd lurching behavior is still there when I execute in slow-mo but seems somewhat dampened.
This morning I changed my stepper settings to half step to just get some more torque until I figured out what was going on, so its not really an apples to apples comparison, but this is a promising lead.
Thanks for mentioning