Looks like you're clutch is on its way out ,Had the same issue with the SR ..Try and avoid the longer pin as sometimes it leaves the clutch semi-engaged,That could be your issue ,what i would suggest is change the piston in the slave to a longer one , The sloyota's have the same diameter if im not mistaken..one from the old box corollas might be an option.
@ sly trust me im so gatvol of this gearbox story,first gearbox smashed into pieces lol well with abit of hard driving but ...thats another story for another day ,i think the normal sr20 box is a feather to lift up compared to the fatboy one
But now it looks i can finally take her for some tuning

And turn up the boost as well,
Will try and document the build on a new thread abit later
seriously impressed with the power though(my opinion it makes far more power at the stock boost than my det at 2 bar)
Only one problem i see ......I DONT HAVE NO TRACTION TILL 4TH GEAR

,My first drive was the best as i didn't expect what would happen when i plant the pedal down."Scared the shit outta me,the gearbox,the neighbors, and pedestrians because we didn't know where the front would face after every gear change" lol