Originally Posted By: HTSS_TR
I would drain and fill, if it has drain plug, every 40-50k miles.
^This at a minimum, as often as 30,000 or more(for a couple shorter intervals) for neglected transmissions.
Another pan drop/filter change and fluid top-off by 250,000 would probably be best IF the car went without servicing for a while, IMO.
Otherwise, stick to fluid changes regularly until the next time the filter is due per the maintenance recommendations for the vehicle.