Assuming the wheel is unloaded, or has a small load, it appears the wheel is not the problem in this application. Maybe I can point you to your problem in the application.
It appears that you are new to the use of stepper motors.
There are a few things with stepper motors that you need for proper operation:
A 12 volt dedicated supply (Unless the stepper ...
If you try to step to fast it will fail to move. If you wish to move a large mass quickly you must accelerate the step rate gradually. Any time you accelerate to fast you should expect the stepper motor to just stop and buzz.