I'm currently building a Prusa i3 rework. I'm having a problem with the RAMPS board. When I only have one motor connected to the ramps z-axis It works great, no whining or skipping of steps. But when I add the other z-axis motor Both motors whine, skip steps and jiggle all over the place. I have adjusted the stepstick to no avail. I have tried other known working stepsticks and connected different motors all with the same problem. What could be the problem? Thanks in advance