Transmission/Clutch Related (Need Help)

[TRISPEEDFD3S]

Alright here goes...

I have an Exedy Hyper Single clutch kit, on a rebuilt transmission with about 30K on it right now. The clutch fork has never been replaced though, and it should have 87 k on that, my master cylinder has never been replaced 87 k on that, but the slave has been replaced 20 k on that, throw out bearing, pilot bearing etc...

Now that I've told you what I have, here is my problem:

My clutch slips and makes a slipping rubbing noise (sounds like a slipping belt) when I give it a little more gas than needed in 1st and reverse. It doesn't do it in any other gear. It will slip then catch and let you go on your merry way. Sometimes it doesn't do it though, usually when I'm driving like a granny or sometimes it just won't do it. I've had my mechanic replace the pilot bearing, throw out bearing, rear main seal, and the o-ring behind the stationary gear, and it solved the problem for about a week, and it started doing it again. He showed me the old pilot bearing and he was curious why it was so gritty like sand.

I'm not sure what the problem could be, but I want to figure it out since my motor went because of coolant seals, and I'm in the position to swap out motors, I want to take action on this transmission problem while she's down. Could it be my clutch? Clutch Fork? etc.... I hope someone whos been through this could help me out. Thanks in advance.

-Jeff