I'll paste what Sergey said after looking at my config file:
"Your axes settings -- those look totally bogus to me. First of all
motors turn very slow at their max speed. Something's fishy here -- either
steps per inch are wrong or maximum speed is way too low.
Acceleration, on the other hand, is simply astronomical
No wonder you
motors are loosing steps. And it was kinda like infinite on Z axis so it was
supposed to go zero to sixty in zero seconds...
I put some rather conservative values there and made X axis a bit faster (Y
and Z are left where they were) so you could be able to test and compare
them.
For acceleration your first shot should be at axis accelerating from 0 to
full speed in something like half second. You can clearly see this time in
Motor Tuning dialog when you drag that horizontal "Acceleration" slider.
Then, if it worked, you can start gradually increase acceleration until your
machine started loosing steps. At this point you back off a bit and you have
your system set for maximum performance. The same is also true for speed."