I bought my '03 in '04 with 10k miles at that time it had a single disk ceramic exedy and I constantly got p300 codes at highway crusing speeds. After getting married and letting my wife drive the car the clutch was shot and needed replacement. The unit I used to replace it was an exedy twin carbon and I still had the p300 still at highway crusing speeds but a slightly different rpm. Well, the carbon went recently and I took it out to be rebuilt and replaced when HP levels actually warrant it. I am currently using an ACT street disk and with over 1k miles I have not gotten any p300's. My best guess is that the code is indeed due to an engine harmonic that is transmitted by the ceramics and multiplate clutches, but is absorbed by the organic single. Hope this helps some people. It has made my #1 PITA go away.

 

that is good to know

 

My p0300 got worse with my act xtss. At least it seemed to, but one thing is for sure. It didn't get rid of it for me.