Hi there, I like your work.
I'm a photographer specialising in reflective subjects. What you need to do, as others suggested, is move the light away from the fabric to create a more even coverage of light on the fabric. With the light too close, it creates a hot spot, almost as if the fabric wasnt in front of the light at all, and this creates the highlights.
You dont need the light opposite, just have a white piece of cardboard to reflect the light back. This will give the gun more of a 3D feel, and not be so flat. You dont need a light on overhead, that will also make it flat looking. One light, used with reflectors, is all you need. You can also put a black card on the opposite side, to give a dark line on the subject - try it, you'll soon see how it looks, and you can experiement with where you place the card to fine tune the look of the holster.
If you still get the highlights, put more translucent material between the light and the gun, like tracing paper, or just a white sheet between the light and the lightbox, to make the light-source, the square of light, more evenly lit. When it is even, the highlights will be reduced or eliminated.
Good luck. Its a learning curve, but when you understand it, the next time it is easy and the results can start to look spectacular.
Corey
www.coreyrankin.com