Marlin 1.0 works: Marlin 2.0 destroys Z-axis motion I have an FLSun 3D Cube, running off an MKS GEN V.1.4 main board. With Marlin 1.0, the Z-axis works great (and has been for three years). When I try to upgrade to Marlin 2.0, moving the Z-axis 10 mm results in extreme motion -50 mm at least, left motor then the right motor, three or four times, very fast. It's loud, it's jarring, and it's at the very least incorrect.
What setting am I missing?
I believe (from reference) the default steps per mm for the FLSUN 3D Cube are:
                                          X,   Y,    Z, E0 
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 100, 100,  400, 150 }

Default marlin 2.0.x are:
                                          X,   Y,    Z, E0 
#define DEFAULT_AXIS_STEPS_PER_UNIT   {  80,  80, 4000, 500 }

Such a setting would explain the excessive speeds; while the printer only needs 400 steps for advancing a single millimeter, the stepper receives 4000, this implies a tenfold, hence larger displacement and higher speeds.