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Try smaller steps, say 35, try binning your exposures x2, reduce your point count to 9 and try 8 or 10 for star size. Really though, you should physically measure your 1000 step movement with high accuracy.
Also, my opinion only, get rid of the Crayford style focuser and use a rack and pinion with back lash compensation. Crayford's are notorious for slippage.
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