Just an update for everyone.
This last week my X started vibrating ALL the time...not just when taking off like the initial shudder. Thought I had a wheel out of round or something that simply needed balanced. Felt very similar. Took it into Tesla and they said it was very odd but they would check some stuff out and sent me packing with my 2nd loaner in 2 weeks.
Got a call 6 hours later that the tires, wheels and suspension were fine so they replaced the halfshafts and jackshaft with the "old" style halfshafts and it seems to have fixed the issue. Sigh.
Even more frustrating news came after they told me that these were some of the worse halfshafts they've replaced and that they've NEVER seen issues with vibration at cruising speeds caused by the halfshafts. Considering how much I've babied this 2nd set of halfshafts, I'm contemplating abandoning ship on my X sooner than later. I still suspect there is a bigger issue with these halfshafts than a bad part.
That said, I'm probably not gonna have any upcoming updates on the new part since I'm no longer in line for them. Quite frustrating. If I do hear anything tho, I'll light this thread up again.