Pmdx-340 stalls stepper motors

[Grant.marshall]

Having an intermittent stepper motor driver issue.
Ex/ z axis up, mid stroke will stop moving, software indicates it is still moving, stepper motor is making noise, feel it vibrating. If I am manually moving z + and keep holding when failure occurs, it will keep vibrating and controller thinks it is moving. If I let off, it will resume normal as motor slows down and then I can continue.
Happened on y axis as well, so assume not stepper but controller.
Running a desktop mill. Steppers are 3.3 volts 2.9 amps. Been running good since retrofit in 2016 until now, 2022. And after restart has fixed itself for now. Any ideas, time for replacement?

[Steve Stallings]

If you feel the motor vibrating or making a squealing noise, then the PMDX-340 is still driving the motor.

Your symptoms sound like the motor's speed or torque capabilities are being exceeded.

Check to see that your DIP switch settings for motor current have not accidentally changed.

Check to see that your software's maximum speed settings have not changed.

Also check that your mechanical systems are clean, properly lubricated, and aligned.