We've been doing mock agility tests for the past 2 months leading up to finishing fire school, and I've crushed a couple for local departments recently. Honestly, with 4 years of crossfit under your belt, if you aren't completely out of shape you should be fine as long as you rest well before the test AND aren't chronically overtrained.
On certain parts of the tests, you'd really benefit from specific training. The Keiser sled (if they have one), and the dummy drag come to mind. Both are events where proper technique can go a LONG way toward reducing your overall time. One local department has a max of 22 strikes on the Kesier or you fail. A strong person that has never had practice could easily fail on that alone. On the dummy drag, finding out beforehand if you are allowed to use an extremity drag could allow you to make up a large amount of time. If not, just sorting out your technique can help a lot... but being prepared for and having practiced BOTH options before test day is by far the best way to go.