Is this another dud board

[erniehatt]

Hi, am trying to set up a GT2560 board on a Prusa i3 printer, the socond one I might add, beginning to think this one may be dud as well.
I have had so many problems, fix one another arises.
Latest one, printed a 20x20x20 test cube reasonable quality, some slight E step adjustments on X and Y, the going to reprint cube I find the Z axis is running at snail pace, barely see it move.
First obvious cause driver, not the case as I swapped it for a know working one no change,
Any suggestions. thanks.

Edit.
I have just made further tests, swapped driver from know working axis, still same problem also swapped axis leads, same problem,
So that tells me it is something other than driver board and motors, that leaves two other options, Main Board GT2560 or a setting in Marlin, which if Marlin I don't know how it got changed, unless accidentally.