You might have recognized that the mosfets is getting really hot on your GT2560 controller. Well thats because the mounted MOSFETs, P55NF06, aren´t the greatest choice. Since they are feed by 5V they are very close to their threshold. Ideally they should be feed with 7V or more.
Replace the existing with IRFB7430PBF wich has lower internal resistance and lower voltage threshold wich gives less heat. They are both TO220 and the same pin configuration.
While soldering and messing around, make sure to rise the cooling element a millimeter from the board, and put some kapton tejp to isolate the circuit board.
Since I bought my IRFB7430PBF from an ebay seller I don´t really think it is original International Rectifier products, but they are good enough for me.
Some useful datasheets