So stage 2 straight through exhaust such as powerflow etc.
Better injectors, turbo and intercooler.
Then remap. Don't forget to get the gearbox mapping looked at afterwards too.
My bet would be on a faulty hazard switch. Id recommend a diagnostic check to see if any fault codes flag up.
This is quite common on the C5 Dave, and it's most often caused by the hazard switch failing as I had similar problems with my C5.
You'll need a diagnostic check to see if any fault codes flag up.
It's probably the roof clamps that has failed. Problem if you can't get into the boot as you could manually control the boot from there.
Had a look online and found this:
https://www.audiworld.com/forums/a6-s6-c6-platform-discussion-58/stuck-tow-hitch-2970418/
https://www.google.com/amp/s/www.audi-sport.net/xf/threads/211403/%3famp=1
https://www.audiworld.com/forums/a6-s6-c6-platform-discussion-58/oem-trailer-hitch-stuck-2931386/
You're most welcome. You need to make sure you get one from the same engine and gearbox as yours as the undertrays can vary depending on the engine or gearbox due to there differing in size etc.