Slide lubricant, bad alignment or not enough torque ?

[dazp1976]

Is that some sort of IGUS bearing (sleeve) I see? It may be a replacement wear part or you my be able to find a IGUS bearing to fit.
Moving the slide without the ball screws should tell you quite a bit.
Gut feeling, with those steppers it's not the slides!
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With the inductance on those steppers, they need DM860 drives and minimum 60v to get decent high rapid speeds.
Proven.
But, never any issue on 36v running at 300rpm with 5mm pitch ballscrews, and my gibs were tight as (mill).