Fix FPS after using speedhack with cheat engine?

My FPS goes to shit for a bit, it's worse the longer i hold down the key, how can I fix this? I think it's v sync or frame cap related since DBD might think it's doing 600FPS per second with 10x speedhack and then tries to do 6 FPS a second instead?

That's indeed because of vSync making fuck-ups after changing the speedhack speed.
You can disable vSync by going to %localappdata%\DeadByDaylight\Saved\Config\Windows NoEditor, and open GameUserSettings.ini.

In that file, search for bUseVSync and instead of True, set it to False.
Then in the same file, look for FrameRateLimit, and instead of 60.000000, set it to (something like) 600. This -SHOULD- prevent the game from limiting your framerate to 6FPS after disabling the speedhack.

No need to set it to read-only. The game shouldn't change these values.