For lighting physics body bounds is the first thing that comes to mind, but i dont think that would be the issue here since you already have it set properly i believe. I also enable Inset Shadows in lighting properties of the vehicle, that also helps. And it’s not a UV issue, trust me. My car’s UV’s are sort of a mess and i havent had an issue so far. 
I’ve been having the second problem as well(i had also mentioned this in my thread.) I managed to minimize it at some point when i was playing with suspensions but then it started to become obvious again as i made more tweaks. Pretty annoying to see my Challenger rise up like a truck when it speeds up. :\