@Shruikan15 As LeeC2202 Suggested in the thread, tuning ids will only be taken from 0 to 255. Any value above 255 will consider only the last 8 bits. To know your actual ID, lets say you have a car with ID 984, the actual value is 216. This is calculated by > Calculator > Programming mode> 984 AND 255 = 216.

I solved all my tuning ID's b following:

Download ID Getter from https://www.gta5-mods.com/tools/vehicle-kit-id-getter Import Carcols.meta from latest updates like gunrunning, biker, importexport etc. See for yourself, which IDs are not used. I think 238 to 255 are still not used. Assign unused ID's to your add-ons on carcols.meta and carvariations.meta as:

(1) carcols.meta
<kitName>254_FeF12A_modkit</kitName>
<id value="254" />

(2) carvariations.meta
<kits>
<Item>254_FeF12A_modkit</Item>
</kits>

You can use ID's from biker DLC, as you may not use much vanilla bikes. By correcting ID's of you add-on cars, should free the ID's thats being used up by gunrunning DLC, which will then enable their tuning.