Randy,
How often do you restart your computer?
One thing i have found with FCP (and this has been on a number of versions) is that it does a poor job of managing your Memory, especially when the project file gets big and you are doing lots of exporting and rendering.
Restarting will clear all the memory usage.
One thing i make a habit of is having the activity monitor (applications -> utilities -> activity monitor) open and the dock icon set to display memory. That way i can see how much RAM is still free and how much is taken up.
I can’t tell you how many times all my memory will be taken up (9GB) i will quit all programs, and there still is memory tide up in the system. I restart my computer, the memory is clear and final cut is back to performing well.
DM