Z axis Randomly starts and stops movement

Hopefully Im posting this in the right spot. I have a prusa i3 controlled by ramps 1.4 and marlin, 20a power supply, heated bed and the 12864 smart LCD w/card reader, etc.

The issue im having is that when jogging the z axis after a few secs of steady movement it will move maybe 10-15mm then stop for a sec, then move another 10-15mm and stop repeatedly until it reaches in destination. It also appears to throw off the DRO some. Its a dual stepper running off a single driver, both are moving in unison, no twisting, no strange noises or "missed step sounds". No idea where to even start. I believe its the A series driver (its about 6 years old). Im considering upgrading to something newer but want to make sure this isnt a bigger issue before i start ordering new parts.

Brian

Sounds like overtemp cutoff from the driver. Did you change the potmeter/current limit? ( sometimes this happens on it´s own )

Check Vref and or/ wire the z-steppers in series, if you haven´t done already.
-Olaf

Unfortunately I don't actually know the amperage of the motors as about 6 years ago I bought a mendal prusa 1 kit from some company ( cant even remember) and they don't have any stickers on them IIRC so I don't know what to set them at. I have some DR8825 drivers with a larger heatsink I'm going to change over to and Ill just set the z axis to double what the x and y are ( assuming they were properly set by the kit manufacturer, they were set at .4v IIRC)

Swapped out the driver for a newer one, readjusted the amps and its working nicely. Thanks! High fives all around.