3d model optimization

I have an Xcarve Pro and am carving a simple 3D model of a 12"x7" very slightly sloped wedge in MDF. The quality is fine but as the head moves left/right in the finishing pass it speeds up and slows down “randomly”.

The finishing path is X raster and the slope goes up in the Y direction so each pass should be just a straight/level run across the piece just slightly higher than the previous. Beyond that it’s hesitating at all, the weird thing is that the hesitation happens symmetrically (same area at the left and right of the pass) and that the location of the slow segment of the path changes as the path progresses along the Y axis.

Brand new machine, fully calibrated, checked all the belts etc and given the symmetry, I’m thinking that it has to do with the 75KB STL model but am not sure what would be causing it to hesitate like this, how to diagnose, and how to fix.

It’s not a big deal as I only have to do this piece once (just about done) but I’d like to understand for future projects. Suggestions? Thoughts?