I was having this problem when I first started adding vehicles to GTA V. I backed up my game, and made myself a Mods folder in Open IV as I was told. I would follow instructions precise when adding new vehicles into the game. However when I would get on, and try to spawn one of the new vehicles, almost all of them that spawned were Vanilla, or a vehicle I already had installed. The only one that seems to be working is the "police" car. I can change that one all the time, but the others don't. This is a problem because I try to download all the big/mega packs. If you can help, please respond!
Thank you!