Matt,
It looks like there is something else running in your database that's eating up resources, like hourly running dbms_job which never ends?
Is your database in archivelog mode and still on NT ( sorry haven't bothered to have a look at init file, it's easy to ask!)
Run statspack and pick out resource eating sql's which can ease your life.

By the way how far you have been successful in tkprofing ?


Cheers