If you'll notice next time you are gifting a car, or any other item, as soon as it says 'upload successful' or 'upload complete' or whatever, it will autosave. However, if it says 'upload failed', the game WILL NOT AUTOSAVE. If you simply quit your game (do not gift anything else until after you quit, or it will autosave), your file will reload before you gifted the lost vehicle, and you can try it again. The fact that it doesn't autosave if the upload fails probably means PD knew this was happening, and prevented it from being permanent, IF YOU'RE SMART ABOUT IT.