In my 1984 GT, I used to change the automatic transmission fluid & filter regularly. And the damm thing only lasted 80,000 miles on it (are you reading this Birddog?) It's not like I was abusing it, it simply wore out. My next 2 transmissions I don't do anything to them ever and neither one has given me any trouble so far (one had 80,000 miles on it when I got rid of it and the other has 83,000 miles on it).
I think if you search usenet you will find people telling you not to waste your money on automatic transmission fluid (unless your into towing, or some other heavy duty activity) because it's not like synthetic oil where at least you get better mileage (if nothing else) from it.