I have a 97 QX4.When driving at highway speeds in overdrive it shifts out of overdrive on its own. It eventually shifts back to overdrive afterwards. it constantly does this. Sometimes it stays out of overdrive for quite a while before shifting back into it. Other than this the transmission shifts fine, but the car cant be driven for long distances on the highway. it has nothing to do with the speed or me gassing it.

Anybody have any idea what it can be or have a similar problem, any input is appreciated

Any check engine lights? When you first start the vehicle does the O/D off light blink numerious times? Something could be wrong with the tranny.

check engine light is on from an evap code and and 02 sensor, which are unrelated. o/d does not flash, and i dont believe its the tranny cause it shifts fine through all gears.

your transmisson computer could by dying. I know that some people have replaced theirs and it made a world of a difference in transmission behaviors.