Just loaded up Euro Truck Simulator, looks to be exactly the same game and I was getting a solid 60FPS(Vsync on and don't know how to turn it off) with the game a full 1080p and 8xAA everything max.
Might be worth seeing if Euro Truck Simulator makes any difference, might be a bit hard to get hold of mind.
Why is yours working and mine not then?

I really like this game too.