With either system, my daughter rarely sees straight up or down arrows, so that may be why we haven't seen ???, but it may also have to do with the Plus. I know that the Dex guy said that they now have the best rate of change out of all of the systems. He was very interested in my opinions since he knew how much we loved the Navigator. The ??? at night would have been a deal breaker for me and I would have been doing what you did and trying to find another Navigator system for her.