I put all my vehicle addons on patchday28, but for some reason some vehicles would not apear in the garage or apear in backup. For example i put two state trooper vehicles in slots police3, and police4. But in the police garage it will only show the default bike. Everything works fine when spawned using simple trainer but i would want backup to respond with my vehicle replacements

You will need to add them manually for the game to recognize them as AI vehicles. Police 3 should already have been added to your garage, and should be found under the LSPD category. The bike is found under SAHP automatically. Though because police-police4 are considered LSPD vehicles, they aren't going to show under the SAHP category. Though you can simply change that. 

 

Go to Grand Theft Auto V\lspdfr\data and find dutyselection.xml. Open this file either with notepad, or a source code editor works if you have one (such as Kate as I am using in the pictures) though that is not required. Just open it with notepad.

 

Go down to the bottom, where you will see a few agency selection vehicles. I have added two lines of code to add between the <VehicleDescriptions> arguments, found in the spoiler. If police3 is already shown, do not add the line, simply change "lspd" to "sahp". Arrows on the screenshot show where you can add them.

 

Spoiler

   <Description name="Police Cruiser" fullName="Vapid Police Cruiser" agencyRef="sahp">police3</Description>

   <Description name="Police Cruiser" fullName="Vapid Police Cruiser" agencyRef="sahp">police4</Description>

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For adding it to agency/AI response, find agency.xml in the same pathway. Again, edit it. police3 should already be here, but I have added the proper coding in the below spoiler if it does not happen to be there. Here, you will be finding <Vehicle>police</Vehicle> in the loadout area. Screenshots are attached to show you where to add the coding I have provided. Again, if police3 is here, do not add it. Simply add the police4 instead. Make sure both lines are added as new lines, not on the same line as other code, or you can risk crashes.

Spoiler

<Vehicle>police3</Vehicle>

<Vehicle>police4</Vehicle>