Background:

Though I'm releasing this mod second, it was my first attempt at scripting. And what an undertaking it was. I owe much thanks to ZAZ, both for allowing me to build this from his T_Trailer_XXL mod and for helping me to finish and work the kinks out. Many more thanks extended in the readme.

Description:

This script chooses and replaces random peds in a random car to behave as police in the game.
The point of this mod is to maintain a certain subtlety. The undercovers shouldn't be hard to find if you know what to look for, but they are meant to blend in. So don't give up. If you can't seem to find them, just get a yourself a wanted level and they'll show up eventually to lend the 'beat cops' a hand in taking you out.

The behavior is mostly scripted to mimic the in game police, though not a perfect mirror.
And they can attack you for trying to steal their car even if you use my Police Immunity script. I don't consider this a glitch, I consider it common sense realism, after all you could blow their cover! 

There are two files in the zip.

V1.0 offers the chance of 45 different cars including FBITRUCK and DUNERIDE
(this option is great if you've replaced these models, or just want to see them driving about)
V1.1 removes the chance of the above two cars, and increases the chance of FBIRANCH
V2.0 Adds new weapons and behavior

Two instances of the same version can work together to create more undercover cops at a time. The two different versions can also work together in the same way.

Please report any bugs here or in the related GTAFORUMS post.