Recently i've been driving and crusing around 45mph, and noticed that my tach is reading about 3,000 rpm, i noticed that it was unusually high, and i counted the gears as my car shifted, and for some reason it just wont shift into 4th gear, it doesn't even try too. And yes i had it in overdrive. I haven't noticed any unusual sounds or any other problems that may bne related, any advice?