If your stepper is not locking up at all then either it is wired wrong or see the following:
Well on my C11G interface board the +CK and +DR are going to +5 volts and the -CK (pin 2) and -DR (pin 3) each go to the input ports on the interface board.
Also if the interface board has limit switch inputs you either need limit switches or you have to jumper those inputs.
Also in Mach3 I had to enaple the Charge Pump, Port 1, Pin 17, Active Low.
Let us know what you find.