transmission

[newell1967]

Digital shift indicater stays on overdrive only and will not go to any other. Anyone have the same problem? I'm wondering if if I have a speed sensor problem also only because when I put the car into park after driving it the idle speeds up then slows and continues to do this until I shut the car down. Transmission shifts fine until third gear. Seems as though right after the tranny shifts into second third trys to come in and slips out till I feather the throttle. Any suggestions will be greatly appreciated. Thanks in advance. westfield, ma.
1989 Olds delta 88 royale brougham 3.8 ltr
440 T4 tranny. 164000 miles.