Stripy Extrusion

Printing appears with a thin gap every so often in the print. The gap appears every 6 to 8 lines and is particularly visible on the first layer in the Y direction. It would suggest to me that there is some mis-match between the gcode and the stepper frequency. Is there a setting in the slicing program that should be set to match the stepper frequency? I use Slic3r

Hy,
First, did you use manual stepper motor voltage (0.425) ? if yes, it’s better to have 0.55v on steppers motors to avoid some problems.