I have the same issue. Manual control works perfect, but executing a program generates this stuttering as if the stepper doesn’t know wich way to turn. And indeed, only in the upward direction, so the tool (or in my case a pen) is driven into the paper. I’m not using the anti-backlash spring.
I have experimented with the current. Initially calculated the value as shown in the video and the explanation. But I have to crank the current up way to much from the 300 mV, up to 1 V, and introduce new problems that way (skipping), and a overheating driver.
I am using the beta software, which is great for x and y. Have done the testscripts. Still a bit puzzled on how to setup the speed slider in Repetier. If I slide this up, I get the same issues on the X and Y axis, which would indicate a “wrong” z-axis value somewhere for our configurations.
I’ll let you know if I find anything.