well I know it s hard doing skins but take my advice.
All cars with BASELIVERY "Matte" aren t Matte in game. So generate "Matte" is like make a full black alpha-channel on all areas you want that "Matte" safe it to DXT 5. You don t need a fresnel or/and a specular map. So take your e.g Ferrari-dds, make a black alpha-channel and save it DXT 5 -that s all!
"Chrome" also doesn t work to me: The Aston Martin looks nice in chrome if you would change your fresnel-dds map reverse. That means a black fresnel means chrome shining on that areas.