I've tested Garry Theft Auto vigorously (I find the gamemode really fun), and I can definitely confirm that there are certain add-ons included - and not included - that can cause problems in-game, ranging wildly in severity. These will be listed below, and solutions to these issues, ranging from messing around with add-on settings to simply picking favorites.


Please share any issues you find, and I'll try to help with them to the best of my abilities, and the problem/solution(s) will be listed here in-order of most important to least. Honestly, given how complex and resource intensive Garry Theft Auto can get? I wouldn't be surprised if this discussion gets flooded...

• Garry Theft Auto causes the game to run very poorly or even crash. We're trying to squeeze a GTA-esc experience into a game from 2004 - What were you expecting? If this happens to you, I recommend running Garry's Mod on the x86 branch or else-wise enabling Multicore, utilizing the optimization add-ons found in the collection and tinkering with add-on settings, namely Background NPC's settings.
  
• Why do I move slower indoors? >:( That's an intentional feature - You can credit Movement Inertia + Indoors/Outdoors speed changer for that. You can turn off the indoors/outdoors speed difference by inputting "sv_dynamicspeed_mode 2" into console.