I have similar symptoms on my A8. After replacing the spark plugs, the problem mostly went away. See, I had engine misfires fault codes & that evidently confused the transmission. With the misfire codes no longer happening, there is still, on occasion, the issues you are describing without predictability. I was concerned I wouldn't be able to accelerate when needed, but as you described, all the power I need is there when I need it most.

Based on the issues I had with the misfires, does anyone know if the coils and/or spark plug connectors need to be replaced at a certain interval? Again, no more misfire codes, but does that mean the coils and/or connectors are still working in tip top order?