yes you will need your marlin firmware of course but what i am talking about is the version of arduino itself which you download from the arduino website. you need an older version. i follow some talk with some developers which is way over my head but this has been a long going problem which no one really figured out what the actual cause was until recently. something about the way marlin is written doesnt jive right with the newer arduino versions so when its compiled there is some kind of bug produced that causes skips if your speed and acceleration are too high. if they are really low you wont see the issue. until it get all worked out you need arduino 1.5.6 or earlier. just double checked that version and its correct.