My mom, aunt and uncle and I took the Voyager cruise last year. By chance, I found a wonderful company that offered private drivers. It was the BEST decision ever! Our very professional driver, Alberto, dressed to the nine picked us up right at the cruise ship terminal exit. We went to Pompeii and spent 2 hours. (I recommend getting a tour here otherwise you'll have no idea what you are looking at. We were able to pair up with another group of 4 or 5 people and we split it, which made it reasonable). Then we went on to Positano (absolutely incredible place), had lunch at La Tagliata (you MUST ask to eat here if the driver doesn't suggest it) and then we ended with some brief time in Sorrento before catching the ferry back to Naples. The ferry takes about 30 minutes versus an hour drive back to the port and allowed us to see Sorrento, too. I highly recommend the tour company. www.aptours.it
Best of luck!