@PermissionToLand Care to tell what car(s) are you trying to use? I can try to download & install them, see if they work on my end.
I used the modding guide I found on this site, installed a couple of plugins, scripts lore friendly cars and even some tanks and planes, all of them work in my game. I'd get occasional crashes from time to time, but that only happens when I abuse menyoo functions excessively. (For example, manually set myself a full wanted level, blow the hell out of those five-o's and then delete everything using clear area function.)