I'm having a similar issue, game stutters terrible while on campaign map but works perfectly fine in all other areas. This happened to me yesterday as well and I narrowed it down to having too much gold (had 65 million due to the woodworking shops). I sold off until I got to 10 million and it was back to normal.
A few hours later it suddenly started happening again and I cant figure out why. One thing I noticed though is that my save from when I first made my character plays just fine, but my recent save at day 683 is stuttering on the campaign map.