Overdrive Light On problems of the 2001 Mazda Tribute

First transmission shifted poorly and when in overdrive would shutter at low highway speeds. Second transmission gave no sign of problem. While driving on long highway trip the overdrive off light began to flash at which time I called my dealer and was advised that this was an indication of impending failure and should bring the Tribute back in for service. I was then informed that the transmission was bad and had to be replaced again. Note: I drive mostly highway and do not tow anything. The transmissions all seem to shift in and out of overdrive alot.