i have a 1998 bmw328i transmission slips after you run the car for 30minutes or more can this be a sensor issue or the transmission is bad? when the car is cold or in the morning the car drives fine i drive it to work and normaly i do 75 to 85 mph and its up hill but on my way back i hit traffic and than thats when the tranmission starts slipping,if i turn it off for half hour it works fine again