Belts and pulleys look right? I’ve heard of pulleys being inside out.
In theory if your belts aren’t seated correctly on a wheel it could lead to a sort of “gear ratio” thing where the head moves faster than expected.
Also in theory if your motor pulley wheels are too big your head would move more quickly than expected. (no idea how that would happen, you’d have to have an incorrect part. I don’t know how large they’re supposed to be, maybe someone can measure theirs and report back)
These are shots in the dark though; I’d be surprised if any of this panned out.
Are you able to do material tests and get reliable cuts with custom settings? #6 on my faq talks about setting up a material test if you’ve never tried it.