My 1996 A6 quattro (auto transmission) started slipping in drive the other day. I can manually put it in 1st gear and it will drive just fine, then shift to 2nd and then upward. Once in Drive, and moving, it will upshift/downshift automatically. But trying to start from still, in Drive, the car moves forward a tiny bit then slips and will thud into 2nd gear around 3,000 rpm and drive from there.

After doing some research I read about the TCM and water damage. I checked it out and the TCM is dry (I took it apart anyway), but the whole underneath of the passenger side carpet is soaked, as is the wire harness. The car did just endure some big wet winter storms, lots of snow buildup, and I don't have a garage for it. So I assume there's some water damage under there and I'm hoping it's an electrical problem, not a transmission problem.

Here were the codes when the diagnostic was run:
00654 Trans range controller signal bad
00518 Throttle position sensor G9 bad signal
00753 Electrical connector wheel speed sensor

All of these codes have since gone away, but was wondering if anyone had any advice on what the culprit could be? I'd love any help/advice. Thanks!