Yes that connection time is fine. As you know you have to clear immigration, wait for your bags to come out, clear customs, drop your bag, get the transit train to the domestic terminal and reclear security.
Any one of these things could run smoothly and efficiently, or they could all be backed up and take an age to get through. You can never tell in advance.
However on a connection like this AA have full responsibility in getting you to Miami. If any of the above factors delay you and you miss your originally purchased connecting flight, they will merely put you onto the next one. AA have a very active and regular schedule between ORD and MIA so there is absolutely nothing to worry about if you do get held up.
