Hello,
Your problem may be due to the specular map being used, a white specmap like the vehicle_generic_smallspecmap will give a shiny, reflective effect on the mesh whereas a grey specmap would give a more matte look. My advice would be to try using different specular textures, I would suggest one but I cant think of a suitable one off the top of my head currently. I hope this helps.
Hey!
I use this website to convert 'Detail' textures into 'Normal' and Spec' http://cpetry.github.io/NormalMap-Online/ all you have to do is click on the left square and open your texture, there are 4 tabs at the top, choose which one you want i.e normal or spec (i believe it is on Normal by default) then you give it a name e.g. whateverthetextureis_n or _s. All you need to do now is hit the download button and you should get the texture in your downloads folder
Hope this helps 
