I have a project I am trying to use SlowCheetah for. I have created my config file (Test.web.config) and all the transformations I want to use (Debug_Mock.config, Debug_SQL.
After a reinstall as described above, I needed to add the subType and transformOnBuild nodes to my csproj file, and it started working for me.
subType
transformOnBuild
Designer true App.config True