I have a 1994 Grand AM and the other day it felt as if my automatic transmission shifted down a gear. Ever since then my car has been reving a lot higher to go the same speed. I also have a loud noise coming from under the hood when I go over 50 MPH, as if the transmission is in a low gear. The noise seems to get a little less when I turn right. I have checked my CV joint boots and they seem fine, no cuts. I have also checked my auto transmission fluid and both the level and color look good. I have also checked the transmission shifting and I can feel it shifting from 1 to 2 then 2 to 3 Etc but it will not go into automatic overdrive. What can be causing my car to come out of automatic overdrive when I was driving it, and to not go back into overdrive ever since?