I gave up on Miami a few years ago...hideous airport. Now always use TPA, tho there's no F on that route. Just over a week ago touch down to driving out of the airport with hire car was 55 minutes.
I have heard that the new arrangements for car hire are excellent @ Miami but it's the immigration queue that always did it for me....awful. Never waited less than 2 hours not what anyone needs after a Tatl.