The DIC in the first cruze's in aus do not show the speed I wish they did! I have tried it with the cruze control on an it doesn't seem to affect that.If you set the DIC to display the speed, what does it show? That would give a clue if it's in the gauge itself or in the data.
Looking over the manual, the output shaft sensor is connected to the ECM. The ECM reports the speed to the BCM and the BCM sends it to the gauges.
So, it could be something messing up the computer bus (got anything plugged into the OBDII connector?) or the output shaft sensor is a marginal.