My suggestion is to forget the organized tours and its
'herding cattle' mentality and instead rent a car in Rome, head to Genoa via Firenze/Florence (set aside some money to purchase top-of-the-line leather coats/goods in Firenze), then slowly head down the the Italian Riviera coast and tour all the way to Naples...then back to Rome.
Suggestion though, while in Rome itself keep the car parked and use the public transportation system...to get around and see the sights. Most drivers in Rome think they should be a top sponsored driver in Formula 1...and are out to prove it.
Being able to drive, will allow you the opportunity to stop as long, or as short, as you like...in any one location..
PS. Do your research and make sure you're OK being there during 'Holiday' (typically in August) as a lot of things shut down...and a lot of brochures either skip over or minimize that little fact.