If it’s like the problem I have it’s not a “frame rate” issue but it’s to do with the simulation rate. Does it seem to run smooth for a split second then stop for a second? If you click on the little color bar thing on the bottom right, does it show the blue one, Lua, using about 99% of the simulation process?
This is the problem I have and it seems to save it with that towns save file. It’s happened a few times to my saves. It goes away with a new game but has happened with 3 games so far. Nothing in particular seems to cause it but I get constant building errors. I only just started playing yesterday so I’m un-installing and re-installing game and graphics drivers to see if it changes anything.
Windows 7 x64 (game in x64 bit mode)
Intel core i7 @ 2.67GHz
Graphics card: Nvidia Geforce GTX750Ti