E230 1996 135k 5 speed auto doesn't want to change gear when cold. I have to take it above 3000rpm in every gear before the gear change takes place. It runs perfect as soon as it gets warm and has been into to 5th (overdrive) generally after about half a mile. From then on gear changes take place at about 1700rpm. I've had the gearbox fluid and filter replaced (genuine mercedes fluid). Any advice please?