First of all we have to clarify some aspects of your question, so we can be sure we're talking about the same things.

Let's check dates first. The "Julius Caesar era of Roman culture" corresponds to the latest years of the so called Roman Republic. Caesar was killed in 44 BC, the republic ceased to exist in 30 AD which is the year where Augustus became the first roman emperor. Defining the "Roman Catholic Church era" is harder because christianization is somewhat fluent. However, in 380 AD christianity became state religion.

So, if you are referring to these dates, you see that we are talking about a span of four centuries and basically the entire lifespan of the Roman Empire. As you can imagine quite a lot of cultural change happened during this period.

But I'm still not sure if this really is what you were aiming for. You'll also have to explain what you mean by the Romans behaving in a more "Italian" way, because (as you admitted yourself) this can mean pretty much everything.