I only throw my in OD when I'm on the highway - I don't want my car to shift into 4th at 45 (it will), and then have to tap the gas to shift back down to 3rd. It'* annoying. I also don't like TC lockup to be an issue in city driving.
that'* why I do D in the city and OD on the highway. Doesn't hurt anything to do it, doesn't hurt anything to not do it...
Anyway, you need to check the scan tool registry and get it on there... we're not going to be able to do very much at all without knowing what the PCM thinks it'* doing.
96 LeSabre (L36)
95 Olds LSS (L67)