@DexLoomer I am curious why you are using this shader instead of the standard mtl_specBump shader. On solid objects like boxes, it does not really serve its purpose.
So, the mtl_specBump does include a specular map, but it is in the alpha channel of the color map.
For me, since I was using the alpha channel to create transparent textures for plants and stuff, I could not use it for specular shading. This shader is specifically made to allow a transparent entity to also have a specular map.