Welcome to the forums!
Unfortunately, I am not sure why you are getting lag on the campaign map. From your specs, it seems to me your computer should be able to handle it (with little effort); and it does seem like a good computer for gaming. It's quad core, right?
I've moved this thread over to the Tech Help forum. There are, also, some resources in this forum which may be helpful. In particular, you should skim the reference guide stickied at the top.
"It is impossible to enjoy idling thoroughly unless one has plenty of work to do. There is no fun in doing nothing when you have nothing to do.
Wasting time is merely an occupation then, and a most exhausting one. Idleness, like kisses, to be sweet must be stolen." -- Jerome K. Jerome
"Some people become so expert at reading between the lines they don't read the lines." -- Margaret Millar
ERADICATE CONDESCENSION! (That means don't talk down to people.)