Tiptronic shift
 

I have a 99 with the Tiptronic shift buttons on the steering wheel. The shift buttons have allways worked fine but just recently they will not cause the car to upshift untill the car has been driven around 10-15 minutes (couple of miles). Has anyone experienced a simular problem or know why this is happening? If the car is in manual the trans will still upshift by itself when the revs hit the limit. Thanks.