Chevrolet Repair: Chevy brake problem, rear shoes, rear drums

Question
So over the weekend my brakes on my truck started acting weird, First it started out as having to be depressed alot more then normal, almost to the point where i could push it all the way down with only gradual stopping power. But now it does that but only of the first push, on the second push i get alot more resistance and a constant hydraulic hissing sound as I apply pressure and maybe only can press it halfway down, then on the third press it wont move down at all and really hisses at me but still stops the car... Then i don't press the brake for a minute or two it kinda resets and starts all over again.

Im a computer person not really a car person so i have no idea whats wrong, It seems like a hydraulic issue to me as thats what the sound reminds me of.  Can you give me an idea s to what it is?  And what i need to do to get it fix?

Answer
Hello Brandon,
The rear shoes are self adjusting, to take up the slack as wear causes extra space.
Your self adjusters may be rusted, and not moving.
I would remove the rear drums and check them.
The hissing is the power booster, and if the rear self adjusters are working, the master cylinder is what I would check next, as well as the power booster.

Van