welcome aboard!
dont forget to read the precat and butterfly faq here:
http://www.b15sentra.net/forums/showthread.php?t=135241
does this only happen in 6th gear? did you bleed your clutch? assuming you are pressing the pedal to the floor yes? the other thing i can think of is the reverse lockout is messing with you going into 6th, maybe do some research on that part.