Clutch Questions

[RX-7 Chris]

I have an '83 RX-7. I'm running a large streetport 12A. I have a RB lightweight steel flywheel. My tranny is the original unit with 215k on it, it has just started getting notchy in 2nd gear over the last 10k. I do have a GSL-SE tranny to put into it that I will be getting overhauled before hand.

Being an '83, I am running the 225mm clutch.

I was running a centerforce II clutch in it from about 150K to 200k and I pulled it because I kept hearing that it would kill my tranny. When I pulled it, it still had life.

I replaced it with an Exedy Stage 1 Street Strip performance clutch. Overall I have not been happy with it. Over the last thousand miles the clutch has started chattering and vibrating at low RPM. The big problem I'm having is in 4th and 5th gear if I try and accelerate quickly over 4k rpm the clutch starts to slip so bad that the motor will rev quickly but the car will not accelerate. This does not happen when at lower RPM, in 1st through 3rd gear, or when shifting between gears. The car does not seem as quick as it used to be so it may be slipping a little when I think it isn't. The clutch has less than 15k on it, I've never had a clutch go that quickly in this car.

Now for the questions:
1. Why would my clutch slip so much in 4th and 5th over 4k rpm only?
2. Who makes the best clutch for the car?

I DD my car so I need a clutch that can handle daily road use.