In my experience, the weather in FL doesn't pose a problem for transmission fluid unless you use your car under heavy loads or long periods of slow movement or idle in hot weather. Look at the maintenance schedule in your owners manual and go by the recommendations rather than some commissioned service writer. I tend to go by the color of the fluid and change it if it shows any signs of changing from it's original red color. I have a '98 Lexus that has 70K miles without a change and the fluid still looks good even though the service writer at the Lexus dealership would like to have me change it every 30k if they could get away with it.