Hello: Changing the Fluid is very nice, but remember that the transmission has also a filter, and 3 to 4 magnets on the bottom of the fluid pan. The filter needs to be changed at least every 30,000 miles and the magnets clean from the metal shavings produced due to the normal wear and tear of the metals. That is why it is so important to change the filter and clean the magnets. I had a Mitsubishi Diamante and the trans was very similar to this one, I used to change fluid every 15,000 thousand miles and filter every 30,000, never had to rebuilt the trans and the car had over 180,000 when I sold it.
C. PR