Saturn Outlook Premature transmission wear

I would like to see if anyone else has had to have their transmission replaced. My Saturn has 47K miles, I have never towed anything and I went to put it into reverse and it wouldn't go into gear. After having it towed to mechanic, I was told the transmission needed to be replaced (besides reverse, 4th and 5th gear were also gone). I have never had a transmission go out...and I do all of the maintenance required.