If everything else checks OK, then I wonder if it's worth playing with the gear lube?
Specifically, the consensus seems to be to run Red Line MT-90 (shared by both the transmission and overdrive). The MT-series of lubricants were formulated to be less slippery than other Red Line synthetic lubricants -- standard Red Line gear lube is SO slippery, it doesn't provide enough friction for synchros or clutch-type LSDs to engage at all. But Red Line encourages mixing MT lubes with their gear lubes to "fine-tune" the slipperiness to your needs.
Perhaps adding just the right amount of Red Line 75W90 to MT-90 would allow the clutch to slip just a little during engagement, without becoming so slippery that the synchros no longer engage?
Note, Red Line also makes 70W90NS -- the NS standing for Non-Slip. 75W90NS is even less slippery than MT-90, so adding NS would (could) make the clutch grab even harder.
(Full disclosure, the company I work for sells Red Line lubricants)