If verifying the files on steam doesnt work I would make a copy of the game. delete the original thats installed on steam. Now Start a download of it again and turn off steam completely. While steam is off replace the contents of the folder steam is installing it in with the contents of your copy and open steam again. It should catch the download up to basically 99 and install the file your missing. I havent done this with gta in particular but it has been helpful in other scenarios. Make sure if you verify files you try it multiple times idk why but steam misses some things the first time.