Extremely low FPS when playing mods like Zombie Survival

[Pistac1o]

Hello everyone, i am having this problem for a few years pretty much, so i would be really happy if anyone helped me.

The thing is, when being in a bigger and intense fight, my fps drops from 60 (locked even if fps_max 300) to like 25-15 and Gmod becomes almost unplayable.
It is only happening in some mods, but in Zombie Survival mainly.

Here is what i think. Or more like what i do not think..

I do not think that the Gmod is running trough my Graphics Card, instead, it may be running on Mboard integrated intel card. It may be happening because gmod is not so demanding game, like, you can run it on potato. So my external Graphics Card will not even turn on when playing. I tried setting everything on maximum, optimizing the game on GeForce Experience software. Nothing worked, not even 5fps more.
PC SPECS:

CPU: Intel Core i7 2600 3.4 Ghz (Overclocked to 4.2 Ghz)
MOTHERBOARD: Asus P8 P67 PRO
MEMORY: Crucial Ballistix Tactical 16GB 1800 Mhz DDR3 
GPU: ZOTAC nVidia GeForce GTX 970 4GB
CASE: Cooler Master Elite 430

zs_port_v50001.tga

zs_port_v50002.tga

If anyone knows the answer, or is able to help me somehow.. contact me please, i will much appreaciate your help.

[Trackster]

Gmod is not running through your Mboard card. If your Monitor is connected to your GPU the GPU WILL render the games. I never saw a case where a pc renders wit hthe intel CPU, even tho the monitor is connected on the GPU.

Have you asked other Users in the gamemode if they get such a low framerate too? Zombie surviva is a gamemode with ALOT of zombies, and gmod is reaaally bad at rendering alot of entities/ragdolls etc. at once. For example i have a i7 2600 too and a RX 480 8GB GPU. When i spawn just a few npcs (30+ or so) im getting a heavy fps loss.

[Socram]

Lol why did you upload your pictures are Targa of all formats?

[Pistac1o]

All screenshots made trough Steam are saved as TGA now, idk why tho

[Trackster]

no they are not? My gmod and everything screenshots are always jpegs

[Pistac1o]

Ur probably right, it is because a lot of people and zombies.. I also set some performance priorities on my GPU, and it is a lot better.. even that 60fps lock is now gone, ty for answer and opinion

[Trackster]

Try F5 instead of F12