Weird Stuttering (Gmod)

[Saturnity]

Alright so, I had an R9 280x BDDE, and i randomly get microstutters, where the game drops to like 0 fps for a split second, and its so annoying because it makes the game hard to play. I then upgraded to an r9 390 and I still get the same problem. Not sure what is going on, doesn't do it in any other game

Full specs:
i5-7600k
z270m mortar
16GB ddr4 2400mhz
r9 390

 

[Anonymouselite5]

Get that as well, but I've just put it to Gmod.
Usually it happens for me when an add on has just finished downloading and gets processed or something. (enabled/installed?)
If you can log HDD usage at those times, for me the HDD just goes full load for about a second. Sometimes it also just happens at the beginning when you load.

As long as it doesnt happen in other games I'd just put it to a Gmod thing or a certain add on that's doing it.

-Also to note it still happens on an SSD and others machines.