617890

It sounds like an issue with lod's. I would check to make sure you overwrote the police3.yft, and not just the police3_hi.yft. If you overwrote both, do a search using openiv for police3.yft, and see if it happens to show up in a patch folder more recent then the one you are editing.
 
I would gander that if you spawned the vehicle in, and then moved far enough away, it would switch to the version you are seeing the cops driving around in. It takes a second to switch between model's, so the cops will be able to get closer then the actual distance the high lod model kicks in as they are actively moving.
 
Alternatively, try installing Albo's modding pack, and placing the models there.