My tt with a 6 speed, triptronic trans started to slip going into 2nd and 3rd today. Also shifts hard when it gets warm. Has no codes that I can see. If you use the manual side of the shifter, shifts good. Has anyone had this before. I figure a sensor, but have no idea what one.
i had similar problems with my 03. i changed atf and filter, but that didn't fix it. after researching on audiforums and vwvortex, i discovered that the shift solenoids wear out, causing hard shifts and slippage. i ended up replacing the valve body with a rebuilt and updated valve body from Revmax.
Problem solved at 170k miles. hope this helps