Meshes look like splitted and overlapped

Hi, I'm building a level using unity, but when I have more than 5/6 buildings and I move the head looking at them the meshes look like they were splitted: a bit like I'd be drunk, I see two doors overlapping. I'm using a GTX660Ti, GpuZ says that I'm not using more than 50% of cuda cores. If I use the keyboard or the mouse everything is OK.
Can someone help me? Thank you!