Y axis is making X axis stall...!!

[Jonathan]

If so then it's very likely your way under voltage and just simply running out of torque, the torque drops off very quickly when wired series.!#

However, for completeness, the torque when wired in bipolar series is greater at low speed than the same motor wired in parallel.

It looks like in Steve's case it's the Y/Z axis motors that are in series, and they're not at fault. Still worth trying, as long as the power supply can take it.