I have recently made some changes to my agenda slicing our time in Rome. We are not city people and want to be in Rome only long enough to see Ancient Rome and the Vatican. Your advice would be greatly appreciated... We are thinking of driving from Castellina to Chiusi, dropping off our rental car and catching a 9:49 AM train into Rome (arriving at 11:13 AM). We would then have to drop off our luggage at the hotel (Villa San Pio on Aventine Hill)before spending the remainder of the day exploring ancient Rome. We would have the full following day for the Vatican and whatever else we chose to see or do. Originally, we were spending an additioal night in Rome and giving ourselves two full days, but with car pick ups and drops offs and travle from Vencie, we would only by leaveing ourselves 3 full days in Tuscany/Florence. I don't want to feel pushed during that portion of the trip.Is this doable or insanity???

It's doable - I forget the time of year you're going but assuming it's spring/summer (with longer daylight hours) you could do the Forum/colloseum the afternoon you arrive and the Vatican the next day - just make sure you check the Vatican's hours.

One note, we took at that 9:43 train from Chiusi and it was packed. We ended up standing in the hall (see my profile picture). So, I'd recommend getting seat reservations before hand.