For Naples I would recommend All Around Italy and an itinerary to include Positano, Sorrento and Pompeii.
For Sicily I would definately go to Taormina. I have used Sicily Limosine service and would highly recommend them. Tiffany is the office manager I dealt with to book our tour and she absolutely one of the best in handling details and getting back to you promptly. Claudia was our driver and he was a gem.
Been there - done that:
2005 Holiday, Sensation, Conquest,
2006 Conquest, Celebration, Holiday,
2007 Freedom Grand Med, Holiday
2008 Fantasy & Sensation,
2009 Fantasy, Holiday & Dream Grand Med
2010 Fantasy and B2B Elation
2011 Monarch of the Seas
2012 Booked - Breeze from Barcelona 12 days