I have a 91 legacy with a 4 speed auto trans. I had the tranny put it not long ago and it worked great for a couple months. Then one day just like someone fliped a switch it only has 3rd gear and reverse. And when its cold and your going down a hill over 40mph it fells like it keeps jumping into reverse. Could this be a shift cellinoid? My tranny fluid is clean and no burnt smell.