Installation involves several steps and requires some familiarity with modding tools and the structure of GTAV's files.
Remove conflicting script trainers and stick to a single, verified menu like . Safe Downloading Practices Gta 5 Replace Car Pack V-1-1-oiv LINK Download
Select the mods folder, not the game folder. Install: Let the installer finish copying the files. Gta 5 Replace Car Pack V-1-1-oiv LINK Download