I've had mixed luck with replacement clutches..OEM saves having to question where the issue is.
Since you didn't mention slipping on start from stop we can pretty much rule out the centrifugal.
Sounds like to covered all the bases, correct oil, soaked the clutches, adjustment...etc.
The discs may just not be to OEM spec thickness!! This happened for me on one of my 350X clutch jobs..took it back apart and put OEM in and it solved. It's a tough lesson to learn..
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)