It has also been suggested at 4 years as well by TT on here. I had similar issues to what you describe with the cold hesitation in gear change and poor down shifts in manual. mine is an 05 and had 32k on the clock, having it serviced gave an improvement, but the biggest improvement came from getting a basic reset done on the box, which forces it to re-learn the shift points and clutch control, its now a hell of a lot smoother and manual paddle shifts are much better.
Basic settings can be done via VCDS or I would suspect you VW garage, since its in warranty I would certainly ask them to investigate, that way you have DSG logged as a known fault during warranty period which could be very handy should you experience any issues later in its life.