Ahhhhhhhhh! The old chicken or the egg thing, which came first.
You stated that this popped up after you changed the ring and pinion set.
What you have described sounds like gear noise, Cruz'n speed is the worst.
Your vibration could be a bearing going bad causing the gear to go out of proper engagement. Check the grease for metal.
Gear oil was clean when we re-checked for contact pattern and gear wear. That was after about 600 miles. The timing could be coincidental. Vibration wasn't immediate but soon after.