I have a 2002 Audi A6 4.2. The car has trouble shifting into gear ONLY after the car warms up, most often occuring when I begin taking off from a stop or attempting to accelerate after slowing down. When the vehicle is unable to shift into the propper gear, the car kicks into a low gear and the gear display background turns red… I am stuck in one gear at this point. I noticed too that the ABS /Traction control lights go on after the car KICKS into gear.
You are describing the failure of an automatic transmission. You should check the fluid level, and add fluid if it is low. Even have the fluid changed and the filter changed. But I think you may need a new tranmission. Hope I’m wrong.