First off, FLL-SJU and SJU-FLL are domestic flights.

After your MEX-FLL flight, you will go through US immigration, collect your bags, go through customs, and then directly after customs should be a place to drop your bags (which should already be tagged all the way to SJU - if you decide to check bags). You will then proceed to terminal 3 for your next flight, go through security, and onto your gates. 2 hrs should be enough time.

On the return, your flights should all be from Terminal 3. So when you land from SJU, you will just proceed to the gate for your next flight - no need to collect bags or go back through security. 2.5 hours will be more than enough time as there really isn't much to do in the terminal.