Yes, I am very familiar with these cruise ports of call and this is very easy. I just helped plan the same exact tours for my cousin and his family. It's an easy train trip from Citivecchia to Rome. Once there, it's a bit hard to get around because the sights are so spread out but if you just visit the Colosseum, forum, Palatine Hill & the Campidogio, they are all right next to each other. They are easy to access on the Rome metro from the train station to the Colosseo stop. You have to take a bus from there to get anywhere else, though it's not too bad a walk to the Campo Dei Fiore & Piazza Navona. There is a hop on hop off bus now that you might try. It's a bit trickier getting to Firenze & back on time. Does your ship leave at 6:00PM? The trip takes over 2 hours and Firenze is all walking. Fortunately, once there, all sights are very close to each other but the city is always crowded and some streets are just clogged with tourists and American students. Getting from Naples to Pompeii is a piece of cake. Their local train, the Circumvesuviana train, goes all the way down the Naples coast to Sorrento. Pompeii is just a few stops along the route. The trains run constantly and are cheap. There's plenty of time to do this in one day. You could do both Pompeii and Herculenaum in the same day. I love Herculenaum. It's much smaller and more intact. My cousins went all the way down to Sorrento for lunch after touring Pompeii and still made it back to their ship on time. The only scary part is Naples. It's a crime ridden city with over 50% unemployment. To get to the Garibaldi train station from the port you have to take the metro, which can be confusing and watch out for pickpockets, or a taxi, who might just take you on a 2 hour joyride and force you to pay him all your money. I recommend the metro. Just study the map carefully so you don't get lost. Once inside the station with hands on your pockets make a run for the circumvesuviana train.
