RPM fluctuation while driving at certain speed
 

Hey there,
While driving around at range from 60 to 80 kilometer per hour the rpm jerks or fluctuation a lot.
Feels like car want's to go ahead, but something is holding it back a little. Once you get over 85 works great. Doesn't matter if the car is warm or cold.

This is how it kind of feels, but only when accelerating - [MEDIA=youtube]kdmL68HIBVE[/MEDIA]
It only happens when driving at around that speed. If I floor it, then there is no issue and car gain speed smoothly. Or if I use S on multitronic, then the jerking isn't as noticeable and feels more smooth.

At service guy told me the ERG is clogged and needs cleaning, but couldn't tell me why there is such issue. There were no other errors thrown out.
I really do hope it's not torque converter as it can be quite expensive to replace.
Will bring the car tomorrow to another repair shop to see what they can figure out.

Anyone has some guesses or similar issue?