Inaccurate Outside Air Temperature reading

Are you sure there isn't dirt blocking the sensor? You could also check if it's getting a dedicated voltage

 

You can calibrate it a bit with Techstream (Mini-VCI) but not enough. There is probably something broken.

Temperature display is slowed down a bit on purpose so that it would not fluctuate so that’s normal.

Sensor is NTC so bad connection somewhere would cause the too low of a temperature.

One way to test if the problems is in the sensor or in the car is to short circuit the temp sensor. By connecting the wires that go to the sensor to each other. Outside temperature should display 60c or 139F. If it does then the sensor must be bad. If it doesn’t you can check what the voltage is at control unit. If the voltage isn’t correct there then you need to check the wiring.

 

All modern vehicle sensors operate on ultra-low amperage and typically only 5 volts. This means that any damage to the connectors (scratches, spread terminals, etc) can cause voltage drop in the circuit; there just isn't enough electrical power to get the signal correct under adverse conditions. Corrosion is one of the most common problems and generally requires the "pig-tail" to be replaced that connects the harness to the sensor.

Unplugging a temperature sensor, checking the temp then shorting the two sensor wires together is s good test. If you get the expected values, it might be that they sold you the wrong sensor.