2003 TT with 180 hp eng, Tiptronic trans
Bough car 2 years ago at about 60k miles; now up to 75k.
Did some service to try & fix a misfire problem - replaced plugs, air & fuel filters, and ran some Seafoam through vacuum line to clean injectors.

First test drive after this, the trans starts acting up; about 3 miles out, it suddenly stops working - daughter said it was like "driving in molasses" - no acceleration, really slow. Stopped & restarted, then it takes off OK but won't shift - went to redline in 1st gear. I drove it an hour later, it upshifted OK, but when it downshifted it would "clunk" into gear - hard.

I'm about to change filter/fluid, but I'm wondering if anyone out there has experienced these symptoms - and what ws the solution?

Also, I'm wary of "coincidences" - any way my engine service could have triggered this issue?

 

I would honestly re-trace your steps with all the service you recently did. Could likely be something very simple especially if the car shifted fine before you worked on it. What plugs did you use? Also did you disconnect the battery? Check battery voltage and cable ends to it. I've heard some funny things happening when messing around near the battery especially shifting problems. Keep us updated for sure !