I think you are talking about coming back to the states. To board a US flight you will get your bags scanned and go through the interview process at the gate. I think the OP is Leaving the US in route to FCO so he should only have the Passport swipe and no bag scan.

One hour should be fine. I did FCO twice last year with a short connection and a long walk. At the hour my flight got in from DTW I don't think there was much shopping available anyway. The airport was kind of dead. I got to the gate well before boarding started. Just make your pit stop at the on board lavatory before descent starts if possible and then you won't have to make that stop in the terminal.

I think some of the Passport Control officers in Europe are "retaliating" against US citizens and trying to slow down our processing to mirror the way that European and other countries visitors are treated when arriving in the US. They just do not do a very good job of slowing it down in Europe. That is just my guess.