I can not, for the life of me, figure out why my rpm's go up, then down when I hit my brakes...plus my brakes go soft. I changed my master cylinder, bled the system, booster vacuum line is attached...HELP!!!

 

possible diaphram leak in your booster.

 

Bleed system again check for leaks.

 

Could it be voltage drop from the brake lights being on?

On one of my order cars, any electrical accessory being used at idle would affect the speed of the engine because it affected the amount of torque the alternator would pull from the engine to generate the necessary power. That car was carbureted, so I ended up making sure to set the idle speed with the headlights and/or heater fan turned on.

Your car should handle idle issues better, being fuel injected, but it's still something to look at.

The amount of power assist to the brakes will change with engine speed changes. A little of that is normal. I would check the idle speed issue first, then check the power brakes after you get the idle figured out.