Sorry to hear about your issues. I'm running an RXT with the lightened flywheel. No issues at all. I've had quite a few cars over the years and to be honest, this divine setup shifts with better, more precise feel than my Boxster-S. No joke. Tremec knocked it out of the park with this one.
Rotational grinding? Have you gone back to the basics and checked the rotors/pads and condition of the wheel studs/lugs for looseness? You're probably better than me, but I've had a fail in the basics category on more than one occasion- and that makes me very humble when it comes to this stuff...