FallenOfficer

Not sure what you mean, but you're able to change the coronas. Take a peak at the ELS keybinds, I believe it might be ALT+2 to change the "tail light" coronas.

Reinstall 686Callouts and make sure you install all necessary files with it. You may have put files in the wrong location.

The underlined section will go into your Main Directory, where your GTAV.exe file is installed.
Plugins obviously goes into the plugins folder which you have figured out.
If your problem still persists, he even included an Installation + Details file. That explains everything related to the callout pack. Hope this helps!

You need to go into OpenIV and go to the meta file for you vehicles.
Once you have OpenIV opened, follow this path:
Grand Theft Auto V\mods\update\update.rpf\common\data\levels\gta5\vehicles.meta
 
To make sure you can edit, make sure this box is highlighted:

Edit the file and look for the vehicles that are disappearing. (Police, Police2 etc...)  
 
You'll see something like this:
<lodDistances content="float_array"> 15.000000 30.000000 70.000000 140.000000 500.000000 500.000000 </lodDistances>
And all you just need to do is change the values to this:
<lodDistances content="float_array">         500.000000         500.000000         500.000000         500.000000         500.000000         500.000000       </lodDistances> Then save and launch your game!
I changed all my custom police slots to that and I've never had an issue afterwards.

Solved it on my own, I'm pretty sure it was EUP causing it to crash as its the only thing that changes clothing related items.