Swiftaw is right. You have to do all the customs and immigration paperwork at your POE in the US. Which means you collect your luggage and go through Customs Inspection at that point. It's no different than when you went to Tampa. You will be able to re-check your bags just past the Customs site. Since you are in the US you will yourself go to a domestic terminal to connect. 3 hours is more than enough time to do that comfortably. Since you're on Delta in Business crossing the water, I think you'll be able to use their lounge while waiting for a domestic flight.