transmission goes into safe mode often but stop doing it for weeks at a time.

You could be having an internal transmission problem developing, especially if changing the fluid made a difference but there are a lot of things that give feedback to that system. Does the transmission "D" light blink, or is your check engine light on when the problem starts happening? There are speed sensors, a transmission control module or you could be having an issue but from my experience it's something internal within the transmission. A bad speed sensor is common on this vehicle, and this would be best least expensive case. I would have it professionally diagnosed.