It’s a rack and pinion drive on X and Y. I have it pretty honed for lash and play.
I will add changing the slicer to the list of things to check, but would you not think that a problem with the gcode would show up in the same place each time?
I did get the vrefs looked at. I watched the vid from Polulu on your RAMPS section – I hadn’t realised that the DRV8824 is only rated to supply 1.5A at 12V, so all vrefs are now 0.7V.
I have a spare stepper as a next thing to try.
I believe the designer of my printer probably supplied the kit with 1.7A steppers because the construction requires some power. The bed moves in the x-plane, and is quite a bulky thing. Mine is well tuned and lubricated though. I suppose that’s why the steppers run so cool, the drivers are rated at below the current of the steppers.