It's really tough at MIA now especially if you don't just have hand baggage. My wife flew in from LHR yesterday with 1 hour 30 min connection to Barbados but missed it by a mile due to queues and the need to pick up her bags for re-checking (a new rule for UK/international connections). A real pain as she's had to overnight in Miami. Try to get by with hand baggage - it could make all the difference. I had no trouble last week with a similar connection and only hand baggage.