X carriage "vibrates" on small segments
The overall torque, and thus the incremental torque is less with your new stepper, this may result in less smooth operation because of moving the weight of the carriage (e.g. when you have a direct extruder mounted on the X carriage). 

You could be facing skipping steps, resulting in less accurate prints. Maybe the Vref has not been adjusted correctly, or the stepper is just not working for your application.