From what I can make out, you have plenty of time here, so long as your CR flight departs on time or isn't more than about 2 hours late arriving. I would assume an hour, maximum, for CBP immigration and usually less than that for TSA security inbound. It's not really a connecting ticket, and I'm sure you are aware of the risks if you don't make it on time. If you aren't one for risks then you would need to plan a night in MIA, or work out a way to get the trip on to a single PNR. I would be prepared to take this risk, but we are all different in respect of risk management.