Need a bit of help.

[Kitwn]

If you haven't found anything and now it works after moving wires etc then it's possibly a wire that is starting to break but not quite there yet. It will however 99.9% be one of the DIR wires, it's a common issue though usually, it's a loose connection rather than a broken wire.

Regards how fast each axis moves then all you can do is keep increasing the motor tuning and acceleration on each axis until the motor stalls, then back off 25% for a stable system or less if you want to push the edge.

Dean,
Does it make sense to set acceleration deliberately low to find the max speed, back off from there and then bring acceleration up afterwards?