Depending on what size trailer and it's load, what types of roads you're traveling (which will impact the types of traffic you'll encounter), any additional tow vehicle loads and/or modifications, etc, I would probably not use overdrive.
With that being a "new" trans, what does your warranty say? What does the trans shop recommend?

On level highways you should be OK. Don't use overdrive if you are on hills. I learned the hard way. The 4l60c in 89 K1500 died a horrible death pulling my car hauler on a warm day.