If you have 3 hours between landing and taking off, I would be surprised if you actually make the connection. Firstly, you land and, if lucky, you will be on time (Once, in Puerto Rico, the plane was on time but the plane occupying its gate hadn't left. We taxied round the aiport more times than a bedwetters tumble drier). When you get off, you will have a long walk to immigration where you will be subject to fingerprinting, questions and checks. (In Miami last year, my wife was detained for an hour without explanation before we were let go). Assuming they let you in without delay, you then go and get your luggage (assuming its there - my luggage went astray coming from Hawaii because they took too long doing security checks and it missed the plane I was on) before you go through customs. If you get through it without trouble, you can then try to find your check in desk for your next flight. If they haven't closed it, you can check in and go to the gate virtually immediately in view of the extra security checks. On arrival, you may have to present your luggage for further checks and told to collect it from the other side of the airport before you check in (happened to me twice in Orlando, one time they told me the wrong collection point, cost me 2 hours). And if they tell you when you get on the first plane that your luggage is checked through to your final destination, don't believe them - Mine was still waiting for me to pick it up at Bangor, Maine when I was in Chicago.
I hope your trip goes well and none of the above happens to you. It is more likely however that you will not have spare time to shop.