for what it is worth I recently got a low miles 760 turbo wagon with a loud/hard upshift from 1st to 2nd.

I understand that one of the check balls in the AW causes this when worn.

But I have had a big improvement with the following...got the IPD auto trans fluid change kit, changed fluid to the "high milage" varnish removing type (Penzoil?).Some improvement and what came out was disgusting.

Then I drove the car about 900 miles, 700 mile road trip rest in city. Afterwards did a complete drain and refill using Mobil One ATF.
I just drove the car from Richmond, VA to the far side of Kentucky and back, up and down mountains, mostly at 78-80 mph... before leaving I felt an improvement, that just kept getting better.

When my wife rode in the car she was "wowed" by the improvement. Still a little hard upshift with hard acceleration...but big improvement.
(PS: also use Mobile One in the engine and probably will do the rear end as well!)