Seems SH5 is funny. Runs fine on some systems and horrid on others.
SH5 ran great on my single core athlon 3500+. with just one small problem....
When i had a large convoy on my hydro, the game would drop to about 2fps...
This was prob because my single core cpu was far below the min specs for the game.
So I bought a new Mobo and CPU. A phenom 965 (four cores) and I had really bad lag, stuttering etc. My FPS were jumping from around 30 fps to 150 fps.
ANTI LAG .dll fixed this for me by locking my FPS to 35.
Now SH5 runs smooth on my system.
I guess SH5 isn't optimized very well.