It's not exactly a technical error, but here's something I believe should be adjusted:
Currently in the mod, you have defined the spawning of Chevrolet Impala in both the vehicle distributions and profession vehicle tables. What this leads to is an all over the place distribution of region-specific versions of the Impala. As you have defined it to replace the vanilla police car, it means that +/- 50% of vanilla police vehicles will be replaced by the Impala. Furthermore, if you continue adding more vehicles to the replacement table, vanilla vehicles will become practically non-existent.
The changes I suggest are as follows:
1) Vehicle distributions table:
Only add 85chevyImpalaSedanPD to it (see below as to why)
2) Profession vehicles table:
Instead of defining additional replacements for CarLightsPolice, make a new entry in the ProfessionVehicles table for 85chevyImpalaSedanPD, and to this entry add all the region-specific replacements. F.e. in WestPoint region - it gets replaced by 85chevyCapriceSedanKSP and 85chevyCapriceSedanWPPD. You can further edit the replacement ratios by duplicating the defined vehicle script references, if that's clear.

About the only downside to these changes is no dynamic replacement of police vehicles on randomized roadblocks. For that, perhaps a separate mod that adds the Impala (and/or any other vehicle you make) to the vanilla police car's replacement entry would be a good idea.

This is an honest attempt that only has the goal of improving the mod for everyone, but whether you decide to follow it or not is entirely up to you.