I don't think I can link it to the service, but mine just improved for the first 10,000 miles of so. FWIW, the improvement in my previous 1400 was much more noticeable.
I get about 50 mpg regularly on the TT. I did do a Y-pipe which changed the character of the power delivery immediately upon installation, but it stinks now at traffic lights. A decent trade-off in my opinion.
Just keep riding her.