I have an 06 convertible JCW that won't change gears (has done it 3 times), but only when I am "getting after it". Shifts fine if I drive conservative (but whats the fun in that!). When it does this, I coast to a stop - car goes into gear just fine - acts normal. Tried cycling clutch a couple times the last time it did it, and pedal feels normal.

Done so far:
Changed clutch master & slave (thought master "could" cause this & slaves seems to go frequently anyway)
Changed shift cables (boots were cracked anyway so it was just a matter of time)

Any ideas?