2002 Audi S8
 

Bear with me as I give you a some background info...
I've read the thread and it is obvious that I will be heading in the tranny rebuilt land soon. I have a beautiful 2002 Pearl White S8 with almost 169,000 miles on it. It makes me almost cry, when I think of getting rid off the car only to avoid costly transmission repairs. About 3 years ago, I noticed a burning smell whenever I pulled in to the garage (which now I think may just be a leaky valve cover gasket where the oil drips on the exhaust). Anyway, worried about the tranny being low on fluid, I took it to a local transmission place and had the fluid replaced. Was told that there was a lot of metal particles in the pan. Maybe a year later I started to experience shuttering when in third gear, going slow up a hill while gently accelerating. This did not bother me much as I did not find my self in that situation too often and knew how to drive the car to avoid it from happening. A year ago, I started to experience vibration at 2300rpm and worried that it may again be a drive shaft and tranny issue, I took it to a transmission shop. Told them about the vibration, the 3rd gear shutter, and burning smell. They found the vibration to be present at 2300rpm at any speed, even when parked. They also found a leaky transmission rear output seal. So...the seal was changed, transmission refilled with Universal Synthetic ATF fluid and (the gear section of tranny?) filled with BG Ultra Guard Full Synthetic Gear Lubricant SAE 75W90, along with ATC Plus Additive. Gasket and filter changed as well. It was a cold day when I got the car back and as soon as I drove it off the lot, I noticed a heavy winding sound. I figured that the new heavy fluids must be thick and just need to warm up - please someone comment on this if you can. This does go away after maybe 5 minutes of driving but the winding is still there a bit if you listen hard enough. That service was done a year and 10,000 miles ago. Now the shifts from 2 to 3 and 3 to 4 are getting worse. If I accelerate gently, all shifts happen smoothly and around 2000rpm. If doing the same but uphill, the shift from 2 to 3 does not happen until 3000rpm (again, I am accelerating gently). If I accelerate hard (hardly do that anymore) the gear shifts seem to happen late and whistling / whinding sound is present. Not sure what to do next.

Definitely get someone who knows what they are doing check / top off the ATF as it's often left low by shops unfamiliar with the procedure. The car has to be running to get enough trans fluid in.
It could also have the wrong filter in it, in that case the pickup neck of the filter is too close to the pan and it starves of fluid. No way to check that without taking the pan off.