a drum brake system has the residual built into the master is approx 10psi. SO yes, while not added...should be in the system. These are usually behind the line adapters of the master body.
With the issue you are having.....and I hate to suggest this given the work you have done but if you do not know what is wrong, prove what is right. I feel each segment of the system needs inspection and validation. You have done the master pretty much, now is time to hand over hand all the lines for kinks, pull and verify they are not stopped up. Including such things as the brake switch T and the rear T at the axle and ALL rubber flex hoses. Ok, sit back now and vent at my suggestion.....I know you are about put out with the brakes and I have probably added to your level of frustration. That is ok, I am in the shop and cannot hear with the noise I am making out there on my own. Remember a flex hose will flow under pressure of the master but return to the master from the drum springs is a weaker push and can prevent flow....HOWEVER if not totally plugged, the aforementioned scenario often cause dragging/locking brakes.