Trade ships could definitely have a lot to do with it- my economy always goes through an up and down cycle, only making money when the trade ships are a certain distance away, and losing when they're not. The fluction of income on distance is pretty big in some cases.
The different sliders though, for government spending and taxes, I'm now positive are not quite right. I'll move the bars back and force trying to optimize the situation, but numbers appear on the right that are not actually able to be gotten, ie, -4 will appear as net total while sliding across, the when i try to return to that place, its -36 or something equally as different. I can increase government spending, and it will somehow cause me to have an increase in my net total on the screen at least, until the next turn, when the value right themselves until i try and adjust anything.
The whole thing seems really off at times... i realize there is the approval level modifier, but this occurs even when the approval isn't changing... hopefully you guys can figure out how to fix it up a bit, make it more robust.