Get on a stairclimber for 30-60 min several times a week. Don't worry about wearing a weighted vest, just up the speed till you're doin about120 floors in 30 min. If at all possible try to use a stairclimber thats like a mini-escalator, rather than the ones with legs stickin out that you stand on. The escalator one is what they will use at the test. Also, don't put your hands on the rail, get used to walking without them on there. It's much tougher that way and you will be doing it that way for the test.
If you're in the gym 5 days a week on a good program the CPAT won't be a problem. I took it when I was trying to get hired a few years back. Quite honestly I thought it was a joke. Both of the other tests I took for other Depts were much more challenging. If you get through the stairclimber part of the CPAT, your home free.
Don't sweat it.
Just found this online, should give you a good idea what it'll be like: http://www.floridafirejobs.org/cpat/CPAT.pdf