Thought I'd share my experience with everyone here. I have a 2015 Model S 85D with 87k miles at the service center getting new left and right half shafts, rear jack shafts, and a new rear drive unit. The jack shafts and half shafts are being replaced due to an acceleration shudder that has been present since ~20k miles, but has gotten significantly worse over recent months. The drive unit is being replaced due to a clunk between regen and acceleration, but this is the first and only DU replacement after 87k miles! The shudder seems to be a common issue, and it is being reprimanded by replacing the half shafts and jack shafts with a new design. For those with the issue, set the suspension to Very High and floor it; the shudder is most prominent on Very High, and this is what I showed to the tech. Love Tesla service, and I'm so glad I went with the extended warranty!