After you find the limiting speed, back off and repeat the test at a lower feedrate several times in a row until you are confident of reliable and repeatable extrusion.
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After you find the limiting speed, back off and repeat the test at a lower feedrate several times in a row until you are confident of reliable and repeatable extrusion. Don't forget to put the printer back into absolute movement mode:
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G90
Enter your reliable feedrate and filament diameter below: