@ smclaren. I think what you're experiencing is the transmission 'disconnecting' via the TC as you slow down, this is a design feature which the VW engineers think we need! Problem is as you have rightly pointed out that if or when the traffic ahead moves off and you also apply the throttle there is a lag that is most likely there to protect the transmission and TC from a sudden change in throttle position whilst the engine is 'disconnected' from the transmission!Really interesting post, Improve.
I've noticed what I think is the effect you are alluding to.
Cruising (and mainly in a deceleration mode) at lower speeds (25kmph - 40kmph), I notice that the motor/revs "floats" ... that is to say throttle response is negotiable/non-existent. I experience this when decelerating/cruising to a red-light, revs dropping, but still moving ... light turns green, foot gently on the pedal but BIG flat spot until the thing spins up again. I'll be more diligent now on getting better stats around whats happening when this 'effect' occurs.
I personally don't think it's as big a problem as the initial turbo lag (for the type of driving I do anyway). I have been doing some very minor snooping around to see if there is a fix for that ... wonder if a more responsive turbo would assist both issues? I am sure you would have a better idea than me, if it would. Thoughts ?
As for the OP's original post I also have a dislike for the TC control tuning, there is certainly a sudden drop in RPM and torque as the TC locks up in 3rd gear and even with the V8 it is still very noticeable and at times quite annoying and somewhat disappointing. Its not difficult to avoid however as I have found the 'sweet spot' in the amount of throttle required to avoid this sudden drop in torque output however this is not always practical due to traffic conditions etc. Sport mode also helps reduce the effect as the transmission will hold the lower gears a bit longer so by the time the TC locks up in 3rd the car speed is higher and the torque drop is not as noticeable. When I'm towing the caravan I tend to use sport mode through towns and and when accelerating back to highway speeds I nudge the shifter over to manual mode and use the paddles, this effectively solves the problem when towing but its not really a viable solution during normal driving around town.
For the record I have a customer with a Cayenne Diesel S and his car does exactly the same thing as the Rline V8, so whilst the transmission tuning is noticeably different in the Cayenne the TC activity is the same.
Good luck with the search and yes you can count me in as a potential 'investor' in a tuning fix...