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I'm getting low FPS too sadly. Not sure what can be done to fix that.

Low FPS

If your FPS are low, it is advised to lower your graphics settings for a better play experience.
If your FPS are very low, your settings are seriously affecting your gameplay.
Low FPS sometimes gets called “lag”, but it’s rarely anything to do with your connection. Sometimes when there is a lot of on-screen action and effects, a system that’s close to the minimum specs may have problems rendering everything and you can end up feeling like you’re watching a slideshow more than playing a game. This happens when your system is under stress and can’t serve up the number of Frames Per Second (FPS) it needs to.
If either your GPU or CPU are below recommended specs, you may really feel it when you’re playing.
Try reducing some of your video settings to combat this. The game may not look as pretty, but it should play a lot more smoothly.

If you have more issue like Microstuttering (tiny shudders and jolts in movement) or Rubberbanding (where your player character runs like they have a rubber band attached to them, and then gets snapped back to their starting position).
Please, precise your problem.

I will try that thank you. However the recommended specs in that link are wrong. Check the Store Page please.

My problem is generally low frames per second. I have about 50 ping usually, a gigabit up/down internet connection, i5-9600k and a 1070Ti

I'm reading what you've put here:

=> Ping: OK
=> CPU: I5-9600k
=> GPU: 1070Ti

Remember, Garry's Mod is a CPU intensive game. But it all depends.
If you look at (for example) hundreds of NPC, props, recently spawned in the server, your CPU will spike, and your FPS may drop (server-sided).
If you look at (for example) lamps, smoke, your FPS will drop because of your GPU (client-sided).

About the recommended specs, thanks for the notice.
I have updated the link

https://store.steampowered.com/app/4000/Garrys_Mod/?