allroad'Ed now

Happens after I have been on the open road for a while (10-20 miles) at highway speeds. I get off the highway, stop to pay the toll (damn IDOT and Chicago "tollway"). When I pull away, the car accelerates through 1st and 2nd just fine. However, when it shifts from 2nd to 3rd, the engine will rev like I hit neutral. Does in in auto mode and in Tip. Does it if I am accelerating hard (WOT) or moderately briskly. Does it whether the car shifts at 4000 or at 5500. Kind of scary when I am in Tip, and run the engine up to redline in 2nd and then shift to third. I have actually hit the rev limiter in this "false neutral" once before it BANGED into 3rd.
Now for the kicker- It only does it maybe once a day. No fault codes stored. And only after having been on the interstate. I can drive around town all day and it won't do it.
Dealer has twice tried to duplicate and no luck. Fluid level is fine. And only upshifting 2nd to 3rd.
Hate to wait until something breaks and leaves me stranded to be able to diagnose.

ChrisS -2008 A6-4.2

My 9210CS started doing something very similar to what you describe @ 132K miles. Turned out that the trans cooler and radiator has fused together-merged and exchanged a small amount of fluid.

Needless to say- $5 grand would have been required to replace the tranny. Just about the value of the car. I traded it off for a new 99-A4 for my wife before it got any worse.

BTW fluid level was right, took it to an ind. shop and they sent it to another shop and finally the dealer came down with the news.