Tranny slipage???

In my 89 A4, I was pulling in the driveway last night and while in D I took my foot off the brake and the jeep started rolling backward. My drive way is not flat but its not steep either. Is it time for a major transmition rebuild? or a bottle of tranny fluid conditioner? What do you think?

Thanks

I think you may have been idling a little low. Certainly not a good test for transmission slippage. Driving it is, not idling about.

And its AW4.