So what are the exact rules for car designs and trademark/copyright? If I have a car very similar to a Lamborghini but not a Lamborghini is the similarity actionable? GTA5 has cars that have instantly recognizable street counterparts (e.g. Ford GT). The rims, engine cover and lights are all markedly unique but still you could probably tell what car my model is based on.
It can’t just be the same car without the logo, it needs to be actually different even if it’s overall similar.
It probably helps GTA a bit that it’s parody
What defines different? Different rims, engine cover, lights, backend, front is different as well. Completely different interior. The side is the most similar but I can change that by removing/reorienting the fins on the roof and side.
What exactly makes GTA5 a parody and why does that give it legal power?
FWIW this is verging on asking for legal advice and you probably won’t find too much of it here. What defines different is mostly up to interpretation (esp. if something ever went to like, litigation - the judge will define different, not any specific law or whatever).
Unless you have a specific reason to be parodying (“an exaggerated imitation for effect”, generally) it’s just best to avoid the whole thing and come up with a unique design. Remember that R* has a lot of high-powered lawyers. You probably don’t.
The rule of thumb I’ve always used is “If I showed this to my mom and didn’t explain the differences to her, would she think they’re the same thing?” If she would, then I know I need to make some adjustments. From what you’ve described, albiet without pictures, (“different rims, different hood, different lights, different front and rear bumpers, different interior”) you seem like you’re in the clear to me, but don’t quote me lol. May as well remove or reorient the fins, if it pleases you.