I have a 1990 Olds CC with 107K. When trying to medium to hard accelerate in OD it hesitates to shift out, lightly stutters until pretty much to the floor and will finally drop down. If I leave it in regular Drive, it doesn't hesitate. My '91's 700-R4/4L60 shudder violently when we first bought it until I changed the fluid and added shudderfix but that was more like hitting a giant pothole. I don't know the last time the fluid was changed, we just bought it last month. I plan to change the fluid this weekend but has anyone had this issue with their boxy before? One other oddity is the last owner had pulled the ECM and Anti-diesel solenoid fuses causing a SES light. When I replaced the fuses it went away and its fuel mileage went from about 8 to 14.5 around town, slightly lower than my '91 with TBI. Not sure if they were related to the tranny thing. Aside from that it runs great now.
The throttle valve cable controls shifts, so first, do a visual inspection. More often than not, a TV cable with a broken end or a broken sheath will cause shift and downshift problems. Do you have performance problems if you manually downshift?
