There is a 2-3 shift solenoid in this transmission. But it could also be an internal problem. It's very difficult to diagnosis modern automatic transmissions from single symptoms described remotely.
The car's computer should be scanned for trouble codes. There is a code for stuck solenoid. If other codes come up, then the transmission should be tested by a professional shop. If you want to play with the solenoid issue, you'll have to get a factory repair manual for this unit and follow the diagnostic procedures outlined.