I removed the backlash and tried to cut again. This time I also had ESTLCAM create pockets for all of my cuts, which seems like it would greatly reduce the stress on the tool with all of the extra small cuts. It still got stuck on retract and plunged. I didn’t hear the Z axis stepper skip (these steppers are pretty strong, so they’re definitely audible when they skip).
I don’t think my Z motor coupler is sliding either, as it is a really tight fit, and then I tightened the screws too. Do you have any other suggestions I might try before I try to print the new middle assembly and see if that fixes it?