My Impala has had 2 fluid exchanges and one filter change in 85k. I had been accused of being anal when suggesting a 36k interval for the Impala. The last interval between fluid exchanges was only 32k and the fluid was shot. I've since revised my thinking to a 24k interval with conventional fluids. I plan on switching to Schaeffer 204S at the beginning of next year and using analysis to establish the interval for tht fluid.
My theory on "flushs" killing transmissions is that a complete replacement of fluid ends up cleaning the transmission out like a solvent based flush would and clogging vital passages. My answer is to do an AutoRx application before the fluid exchange.