Might sound as weird as it is but whenever i change the car with any other but gavril D, fps locks on 19 and won't ever come back to normal. The thing about it is that graphical settings won't even affect this value, no matter if i set them to high or low, the value will still be 19, which makes me think it as a bug. I tried reinstalling the game with no success. Using 0.5.5 version.
Just upgraded to 0.5.6. Issue partially solved. Won't occur with all the cars but the ones with high-poly shapes, which indeed is a cause of hardware limitation. Thread closed.