what am i doing wrong?!

Since I don't own an Aztec, I don't really know; however, reading all the other posts about Aztecs would indicate you should probably be looking for another brush...
Your compressor pressures sound about right. The only thing I can think of is to try thinning the mix a little more.
Gip Winecoff

do you adjust the thumbwheel at all?
i set up by turning mine all the way to the 'closed' setting (no paint comes out) and then work back the other way until i get paint but no spatter while working the trigger in single action.
i have not had much trouble w/ paint build up at the tip.

ed.

That used to happen to me, I did what styrene and william said and it became managable, then all my problems went away when i bought my iwata. I thought I still might use the aztek for quick stuff but found that the iwata was still quicker all around.

One of the first things they teach you when you take an airbrush course is to clean the tip. And they keep repeating it throughout the course. Acrylics tend to dry much quicker than solvent based enamels and when you shoot them through the airbrush they will start to dry on the tip of the needle. If you are spraying a large area where you are continuosly painting you wont notice this problem that much but if you are doing small areas and stopping and starting in between, the paint that is sitting on the tip of the needle starts to dry. Every time you start again it puts another layer of paint onto that litttle blob on the tip. Now the airflow is disrupted and instead of getting a good atomization you get spatter. The solution is keep a small container of solvent or thinner for the type of paint you are using close at hand. After you have sprayed an area (such as a camo pattern) dip a short bristly brush in the solvent and brush it around the tip GENTLY! to remove the buildup. Before you start spraying on the model give the airbrush a short burst of air only to blow the solvent off of the tip. Now go back to your model and spray. I know this sounds kind of tedious but when you are doing artwork with and airbrush and you get splatter you are screwed.
At least with a model you can sand and respray or in a lot of cases just respray. I don't care what type of airbrush you are using, they all atomize air and paint at the tip of the needle and if the paint at the tip of the needle starts to dry you get an imperfect spray. By thinning the paint more will help but even if you are using an Iwata this will happen. I know, I use one quite often, along with a Paasche and a Thayer Chandler and sometimes my old Binks model B single action. I hope this helps.