Well, the board is able to deliver 3 amps into that stepper motor (and it gets those motors damn hot too!).
Tip 1: Setting the motor current: Stepper Motor Current Calculator
Tip 2: Checking voltages FAQ
Tip 3: Is it a Rev 1 or Rev 2 board. It is possible the motor low current enable is somehow turned on. The mechanism is different between Rev 1 and Rev 2.
PRO 1: Idle Current Reduction must be disabled PRO board only – install J4 on all the 8-pin headers when setting the voltage.
PRO 2: Take a look at the Pin 1 enable signal. Did you jumper it? Is your system sending a ‘disable’ signal?
Let me know some more detail.
BrianV