if I coat it over a flat paint it usually comes out satin, so I either usually end up either adding a second coat overall for weathering, or just where the decals will go if I am not doing any big weathering on it...
as far as looking uneven... when you paint it on use a wide flat tipped brush, use a slow even stroke and (what I have done) cover the entire length of the part you are painting if possible.. this eliminated the starting and stopping heavy spots...
you could also try putting a bit of water or alcohol into it to thin it a bit, this would definitely require a second coat I am sure to get it glossy...
Also you might be putting it on a bit heavy and getting buildup along the lowest point of the part you are painting...