I have Spec Stage 3+, URD lightweight flywheel, and TSK45. Installed at 61,000 miles and now at 72,000 miles, it is broken in as far as the "shaking" when starting in first. However, the "chattering" never really went away, especially in stop and go traffic. When keeping the clutch pedal to the floor and in first when I am stopped (instead of pedal out and in neurtal), then when engaging, not only does it chatter, but first engages early - sometimes it is slightly engaged even with the pedal to the floor. Especially when I start the truck, I need to be in neutral; if in gear with clutch pedal in, whan starting I can feel it grab a little.
The funny thing with all of this is sometimes before engaging in first from a stop, if I go to another gear when stopped then put it in first, its a good feel and letting the clutch out in first is excellent (no chatter, no early engage, perfect). Not sure if a bad seal, bad syncro, or pedal adjustment is needed.