I have a problem with my 2002 Jetta GLS with 09a Tiptronic. It goes fairly well when it's cold but starts slipping and harsh shifting after it gets hot (normal 90C). The problem is with the second and fourth gears (more with the second). If I drive slowly then it will be fine but with moderate and high acceleration it cannot catch the second gear properly revs will go high and then BAM! (same with the fourth gear). I thought of installing additional radiator but I would be quite a challenge.
(no error codes at all)