Aye, I play FH with the lowest settings (0 Anti-aliasing and 800x600) in order for it to lag less. I think the first place you went wrong was uninstalling the regular FH; unless of course you just don't want it anymore. FH+ and FH are two different games, you know.
Anywho you might try switching your rendering subsystem.
Ex; if it's on OpenGL, change it to Direct3D9 and restart your game. Or vice versa.