MacBook Pro Retina (rMBP) Running Slow; System Resources unused.

Hey! My Mac runs extremely slow in certain applications such as Final Cut Pro and GarageBand, to the point that the applications are relatively unusable, e.g. waiting 10 seconds for music in GarageBand to start playing after pressing play. However, when observing Activity Monitor, these applications are only using <10% of the CPU, and only a small fraction of memory.

System Specifications are as follows...

2.6 Ghz Intel Core i7

16GB Memory

512GB Flash Storage

OS X (10.8.3)

I've performed AHT, SMC Reset, OS re-install, and an NVRAM Reset to seemingly no avail.

Any ideas what could be doing this?

I have a hunch it might be because I've only got ~20GB free on the startup drive - but as it's Flash Storage, I'm not sure if this is relevant. Also, IIRC, this issue persisted in the past when I may have had ~100GB free.

Thanks in advance! 🙂