Hey, flea. What you're describing sounds like occasional 'clutch jitter'.
Just thinkin' out loud, to give you a few things to ponder:
Engine oil.
Correct type.
Enuff pressure/flow to get oil past clutch pushrod and into hub.
Steel plate tab edges.
May have sharp and/or angled contact edges on the spline tabs.
Stone off the sharp corners.
Steel plate orientation.
Flip them over. Rounded edges to outside, or to inside, your choice.
Basket fingers and hub spline edges.
Excessive gouging/grooving from previous plate setup.
The 8-plate setup will have different/misaligned contact points.
Some clutch plate edges will be riding on fresh surface, others may be trying to fall into, or crawl out of, previous notches.
Plate orientation (because of aforementioned angled contact edges) will affect this.
Non-equal clutch springs.
Sort according to length. Put longest three in every other hole. Kinda equalizes pressures.
Wobbly clutch basket. Check clearances, spacers, proper assembly.
Wobbly clutch hub. More serious.
Wobbly pressure plate.
With trans in 5th gear, pull in clutch lever, have someone rotate wheel, watch pressure plate.
Look for wobble.
Often cured with proper clutch springs, or redistributing springs to equalize/balance pressures.
Take 2 beers, and call us in the morning...
