Linuxcnc wood lathe insufficient torque

Hi
Looking for a bit of help from the more experienced cnc'ers out there.
I am in the process of converting an old Magnum Phoenix EZ CNC wood lathe to linuxcnc. As it was originally fitted with nema 23 steppers I bought a cheap kit off amazon with nema 23 270oz steppers, TB6600 drivers and a 24v supply. Drivers do not seem to have enough torque as it may turn a bit but then just jitters. Woret on the long z axis.  I purchased a 36v supply and a pair of 425oz nema 23 steppers.
Neither increasing the power supply voltage alone or switching to the 425 oz steppers seem to make any noticeable difference. when it is stuttering ie not turning, it only takes a little bit of help by turning the screw with my fingers to get it moving and I don't notice any difference in the amount of help it needs with 24/36 or 270oz/425oz.
I have reduced the velocity and acceleration in stepconf and while slowing it down seems to help it certainly does not fix it.  Only thing i have not changed is the drivers. Is that the next logical step or is there anything in config I may need to look at?

Off On Off Off Off Off which is 8 steps as I have it configured in stepconf and max current which i believe is 4.2 A with the TB6600. Nothing gets the slightest bit warm. Original stepper was a nema 23 but round bodied and smaller than the 425ox (I only have one, The guy I bought it from had removed the Z stepper and fitted an electric drill to the shaft).

Pic attached
 

The old motor is 8 wire but 3 pairs where joined meaning there where 5 wires going to the controller. Besides which having only one motor I thought i should replace both. What confuses me is that there is no improvement when going from 24v to 36v or from 270oz to 425oz, I would have expected 425oz at 36 to give a fair bit more. I will measure resistance. Thanks for the assistance.
 

The threads are inches. I have tried lots of values. Currently slow enough that you can hear it winding up. Gets it moving but it will stutter to a halt after a couple turns.

48 volt power supply and DM542A stepper drivers would almost quadruple torque you have now with your same Nema 23's