I just had the same issue and fixed the problem this past weekend in about 4 hours. You have lost your overdrive most likely due to broken snap ring that holds your overdrive servo in place. I won't go into much detail as there is already lots of info on this sight to guide you through the repair. It basically entails replacing that snap ring but it's a bit involved (depending on your mechanical aptitude and tranny experience...not questioning anyone's abilities mind you) and the good news is it's really inexpensive if you do it yourself versus a tranny shop (ugh). If you search overdrive repairs here on the forum you will find the info you need. BTW lots of folks say it's ok to drive with the overdrive off but, in my opinion, it's probably not very wise to drive around with broken metal pieces inside your tranny...especially in the valve body channels. Mine went out on a Friday, did the repair the next morning and I was back on the road pulling my bass boat that afternoon. Hope this helps.