My PRT4896 has a visible "shudder" moving from any point in X back towards 0. I don't see it when jogging, just at cut speeds.
I did replace the pinion gears a few years ago just before I closed my shop and moved it into my garage. And it has been lightly used over the years since then.
What I have not in quite a while is taken the time to tune-up the machine and make sure everything is still square.
But if this were a problem with square and level, I would expect to see issues with it moving in both directions in X, not just one direction.
could this be a symptom of a motor on it's last leg or a driver?
I have the 4G upgrade BTW.