Sounds like the same problem I have for sure, I wish I could get a tech to feel it, I hope they figure it out for you at least.
I started thinking it was an engagement issue perhaps, maybe I wasn't pushing the clutch pedal down enough during quick shifting, but I don't rip around often enough to pinpoint anything. I have just been marking down in a notebook the times that it does happen, the temperature, date, shift, and rpms.
I feel a less severe vibration more often which feels like the severe on a smaller scale, but the severe ones are the worst. I hate that I can't duplicate it for a tech. I don't know what to do, I hope they give you some answers and I can follow up, I will make my techs call yours and discuss it if they actually establish and document an issue...I am tired of the run around.
Thanks a ton for the update, I am glad to know someone else at least is getting somewhere with the problem.
Did they tell you what they did last time?