Overdrive

The place to start is by reading and recording any diagnostic fault codes. Next is to view live data on a scanner to see if overdrive is being "requested" or "denied". If it's being requested but the transmission isn't going into overdrive, it's a mechanical issue in the transmission. If it's being denied, look at the "Inputs / Outputs screen to see why. The most common cause is an erroneous temperature reading that is telling the computer the fluid temperature is too low to allow overdrive to occur.