Are you using Mach3? If so, S commands will dwell on every line of gcode because those commands are for spindle speed, not laser power.
You will need a 8bit PicConvert board for PWM laser control. The axis letters used are Z, A, B, or C.https://jtechphotonics.com/?product=dac ... rter-board
If you were using the MA3 10bit Analog encoder before, it's a better option. US Digital does sell a 10bit PWM version also.