Hi Carol. We have flown out of Miami many times. We tried the shuttle at the Sheraton once and will never do it again. I think a lot of airline crew stay there and they appeared to get priority when the bus pulled up. I understand they have to get to their flight, but it was stressful waiting 15 minutes for the next shuttle.
We now stay at the Hyatt Place near the airport and drive to the Park and Fly which is close by. Their shuttles are really dependable.
Wishing you the best on your upcoming trip. You sure deserve it after all you have been through.