I'm in the same situation as you ,same Extreme clutch in my GTT running 380hp not on good tune anyways,,did the same thing launched it from 4.5 to 5 RPM and it started making grounding noises ,couldn't get it into 1st gear had to go neutral then second then 1st with pedal pressed down, now couple days before it relly got worse and clutch would sort of hit flywheel similar if you let the clutch go to fast but with constant hitting even in neutral and yesterday it just seized compleately.... could not select any gears and if the car was in neutral it would still move forward until clutch was fully pressed to the floor ......
now have to put my old "HKS twin plate 1000ks.....you hate it and you love it at the same time LOL"