Goto the game library, select gothic3 and right click. Select "properties", goto the BETA tab and set the opt-in bar to version 1.75 cpt. It will download and update the game. This will fix the mouse issue.

First back-up the saves folder C:\Users\<>\Documents\gothic3. Make a copy of the gothic3 folder and place it on the desktop for now.

Open the save folder C:\Users\<>\Documents\gothic3

Delete the old save files except for the last save file with this name G3_World_01_0003.g3savdat (your number at the end will be the # of saves this is my save 3, it's my highest save)
You can copy and paste it from the backups if you deleted all the saves already.
Leave the Shader.Cache and UserOptions.ini.

Run the game, turning off alternate balancing and starting a new game. After cutscene, immediately do a fullsave then quit the game.

Open the C:\Users\<>\Documents\gothic3 again.

You should see two new save files listed - G3_World_01_0001.g3savcpdat and G3_World_01_0001.g3savcp

You want to remove the G3_World_01_0001.g3savcpdat from the folder and place it on your desktop.

Now copy it's name and paste it over the G3_World_01_0003.g3savdat, renaming it to G3_World_01_0001.g3savcpdat.

Start the game again and you should now see the save file listed.
Load it then re-save it over top of itself.

You're finished:D

You should now be running at 1.75, with a fully working mouse and your old save should be working.


Enjoy.:D