0AlphaOmega:
If not, then you have a mechanical problem. Disassembly of big motors is quite easy, you may find that the field windings have broken loose and are able to rotate, although that may be accompanied by a lot of noise while in motion. It may also be a single coil that is defective. This may not be noticed if positioning is via some form of encoder rather than absolute stepping, only when holding would a problem manifest itself.
Don't disassemble a stepper motor - some are permanently demagnetised by doing this and lose torque.
(For the same reason you shouldn't over-current them). Also the bearing alignment is vital to stepping accuracy
so reassembling without calibration may reduce accuracy.
You can check if the coils are intact and whether they are shorting to the case using a multimeter.