mach 3 pockets cuts are 0.5mm undersized always but outside cuts are prefectly accuracte, i have tried both parallel version and the 100 Khz rnr motion controller, i'm using DM542 as my motor controll

This may be an issue of conventional vs climb cutting direction. I would recommend trying the opposite on your inside profiles and pockets and check. Let me know if this worked and what you are using for your inside cuts before the change.