If you're docking in Montego Bay, I have a better idea for you.
We went on a tour with Carolyn Barrett (
www.barrettadventures.com) to Mayfield Falls. They're a little smaller, but it wasn't as far a drive and it was competely uncrowded. There was just one other group on the whole falls.
When we got back to the cabin and watched the video of the Dunn's trip on TV (huge crowds) we were very glad we made this choice.
It was also less expensive, too.
Cheers!