X-Large Upgrade Z axis not cutting right

Just upgraded my X Carve 1000m to the z axis kit so far it has not cut properly at all it is leaving flat spots and lines and completely messing up the cuts. I have had 2 z axis replacements and when I switch back to my old z axis it works fine again. Tech support at a loss? Waiting for them to return my call again. Seems obviously to me z axis is the issue as they probably need to send me another one. Anyone else having this issue? Very frustrating!!!

Ensure the coupler accessed from the back of the Z axis is securely fastened in place. there are 2 small screws that hold it to the stepper motor shaft and to the lead screw and these sometimes arrive snug, but not tight and will easily back out.

Also, ensure the Z axis assembly is low enough to reach the wasteboard with even your shortest bits (usually vbits) … Having depth issues with a '21-'23 X-Carve CNC? See the Simple Fix - YouTube

It kinda sounds like your tram may be off as well, you may need to adjust the angle of the Z axis to correct this issue, ,

Have you verified the movement of your z axis. You may need to calibrate it. If switching back to old and then to new without any changes to setting in grbl then it’s likely the problem. I doubt both have the exact same calibration. Make sure the z is moving exactly the distance you input. This is best measured with a tape flag on the z and a metric ruler. Please let me know if this doesn’t make sense or if I have missed something.