One thing to do regularly on your tansmission fluid, is to check it for a burned or smoky smell. Also, take some off the dip stick, and let it stand on something with a white background. It will give you some idea on the quality of your existing fluid.
Just had the Buick (97 LeSabre) serviced, because my oil change guy indicated it was burned (it smelled funny). Spending $100.00 to get the tranny serviced every 24-36K miles, is much cheaper than the alternative. I've been getting my tow vehicle serviced every 2 years recently.
Tex