Tom said, "there is a 66.6% chance that the three arms of the pressure plate were probably not installed in the same position"
You may have hit the nail on the head. It's kind of hard to explain, but as the flywheel and the pressure plate wear and warp, they wear together, even tho the disc is between them. If you didn't get the pressure plate re-installed in the same position (one out of three), the highs-and-lows won't match up correctly, and you will have a grabby or chattery clutch. I'm sorry to hear this. Will it wear in with use? I don't know. It might be worth a try if you can stand it. Any time I remove a pressure plate from a flywheel, if there's ANY chance of it going back on that flywheel, I mark them both with a stripe of paint or some punch marks. BW