GM Service Manual Online
For 1990-2009 cars only

Performance Shifting DTS Only

When your vehicle detects a change in driving conditions, it will automatically initiate the appropriate performance shift mode. When this occurs, the gear display on the instrument panel cluster will change to indicate that the transaxle has shifted to a different gear. For example, the gear display on the cluster may indicate 3 or 2 even though the gearshift is still in AUTOMATIC OVERDRIVE (Overdrive). Once the performance shift mode ends, the gear display on the instrument panel cluster will return to normal.