GP3, 3.0 tdi, later switching time from D2 to D3 at cold temperatures and cold engine

Hello, I’ve noticed more than once that my fat guy, when he’s still cold and the outside temperature is at most 3-4 degrees, only switches from D2 to D3 at about 55-60 km/h. Is this because of the cold, now probably tougher gear oil, or do I have to call the workshop again? This problem only occurs when the vehicle is cold. Thanks already for your help. Greeting Mathias