Thanks for the reply Bill.
I should have noted I washed the pre-filter thinking it could be a blockage and it still shuts down. It's odd though, because sometimes it will run for two hours or more without a problem.
The pre-filters I use are washable, but maybe there's a limit to that. I'll put a new one in and see if that helps. Here in Lake Worth the water is pretty muddy, but I was having the problem in the Bahamas as well.
I don't have a feed pump, the CAT pump is plumbed directly to the pre-filter.