I have been working with the Reprapdiscount RUMBA for the past 6 months now doing very extensive testing. After a lot of troubles with skipped or missed steps on prints I had gone through almost every possible component to eliminate the issue: - reducing the current on the stepper driver - changing from the A4988 stepper driver to the DRV8825 stepper driver - changing the cables - changing the stepper motor Finally, I have figured out what the problem was. There are defective stepper driver sockets on every RUMBA. On my first RUMBA board, it was on the X socket. On my second RUMBA board it was on the Y socket. If you replace the socket designation with any other available socket (say E1 or E2 in my case) it eliminates the problem. I have to say that I have been very pleased with my RUMBA board so far, but this problem and the fact that the support is non-existent makes me want to change to another board or supplier. I will try Geeetech's RUMBA board next to see if theirs are any better. Otherwise, I'm most likely going back to RAMPS.