Z axis issues

My z axis is suddenly giving me a lot of issues. While manually jogging the Z axis I can give it the up command repeatedly and after the first or second time it will change direction and go down. Then it will change back. I have already completely disassembled the axis several times. I have cleaned all the parts and I have checked all the wires to ensure they have a good connection (I soldered them on at the axis as well). After several hours of trouble shooting, I'm still at a loss. Could this be a bad motor. Unfortunately with the way the wires are run on these machines it would be a real undertaking to swap one out with another just to see if it corrects the issue. Are there any other ideas?

Thanks in advance,
Andy