Need Help! Z axis problems

I'm using Mach 3 with a 4 axis Gecko drive. When I use the keyboard to jog the machine on the Z azis only it will reverse itself (pg up sends carriage down and visa versa). It is not consistent. If you tap the keys it will reverse itself again. I've reinstalled Mach 3 and changed the keyboard with no help.
I'm praying it's not the Gecko drive. It does not happen on the X and Y axis.
Thanks in advance.