Generally Pops if you are having trouble with textures/content in Gmod it is because Gmod is a source game and requires other games for content. Various content comes from a variety of games, MAINLY Counter Strike Source and Half Life 2. You will need these games. If you have them make sure they are installed and you have ran them at least once. Also in Gmod, on the bottom right you will see a small controller icon, click on that and make sure the games are checked so it may receive content from those games.
