Tuning settings are further back in this thread and the comments then said they were fine.

I've now unplugged the motor and been turning the knob to move the Y axis up and down, it's not that stiff really. This is with the leadnut mounting loose, so it's just pushing the gantry on the lip and is free to rock about a bit.

I also tried putting the Y axis drive on the X axis motor and running that and there is no stalling. I tried by hand to give some resistance to the head moving and it just powered through it.

Could I have a dodgy motor?