As I said in the title there is some issue with my z axis steppers. They will make a humming sound and vibrate a little but won't actually spin. I'm fairly sure this is an issue with the firmware (but I might be totally wrong) since they turn when the wires are switched with the ones for the Y axis and swapping the driver board for a spare had no impact on them. Any help would be appreciated. I am using RAMPs 1.4 and marlin firmware.
Try connecting Y-motor to your Z ports. If Y-motor will behave like Z-motors, then there's problem with your Z ports, be it hardware or software. I'm not a RAMPS user, but have heard that there is voltage regulator for every motor port. Sounds like your motors may be underpowered.