because the program is faster but use the same trajectory planner as M3, I had the acc a lot higher in M4 than M3, tuning the acc was the only way I could get it to cut well in 3D cuts 0.001 mm over a 1000 moves. if I did not tune it it was all over the show with 3D cuts, 2D where fine but are even better, it's doing the 2.5D, 3D where you can have problems.