Q: I never get a glossy paint coat even though I am using a gloss paint.
A: Most likely this happens when the airbrush air pressure is too strong, the paint is starting to dry before it reaches the surface from the airbrush. A rule of thumb is that "a wet coat is a glossy coat". You can either dilute your paint mixture with more thinner, or reduce the air pressure.
On the other hand, if your air pressure is too low or the airbrush is shooting too little of the paint, this can also lead to non-glossy finishes. In addition, check your room humidity level and ensure that the air is not too dry. In this case, the paint mixture might require more thinner. I use acrylic paints and I just add several drops of water to delay the drying time. Lastly, always test the paint mixture first before painting the actual kit. ^_^