Hmm, that sounds very strange! The game can be a bit slow to shut down with a lot of workshop content, but not several hours! :S
Try adding the launch options -noWorkshop and -disableMods and see if it's the same with those in place.
How To Set Launch Options
Try adding the launch options -noWorkshop and -disableMods and see if it's the same with those in place.
How To Set Launch Options
- Right-click on the game title under the Library in Steam and select Properties.
- Under the General tab click the Set launch options... button.
- Enter the launch options you wish to apply (be sure to separate each code with a space) and click OK. Should look like this:
-noWorkshop -disableMods - Close the game's Properties window and launch the game.