If the "High Resolution Textures" option is grayed out, the game doesn't recognize the files. Double-check that the files are in the correct sub-folders.
If your frame rate tanks, try lowering "Shadow Resolution" or "Anti-Aliasing" while keeping the texture pack on; textures usually affect VRAM more than GPU processing power. If the "High Resolution Textures" option is grayed
Navigate to your Sleeping Dogs installation folder (usually C:\Games\Sleeping Dogs ) and copy your "Data" folder to a safe place. If the "High Resolution Textures" option is grayed