Hello.
The TB6612FNG should be able to drive a stepper motor. From your description, it sounds like you might have a power issue. Could you tell me more about your stepper motor? What are the rated voltage and coil current of the stepper motor? Could you post pictures of your setup?
The VNH5019 shield can also be used to drive stepper motors. You can find more information about using it to control stepper motors in this thread.
- Jeremy