I have a 1989 4Runner 6cyl automatic. When the car is off, the brake pedal is stiff but if I turn the car on it sinks to the floor and when I'm driving I need to pump the brakes to get a decent pressure. When I pump the brakes it starts to make the car stall.

The recent work done on the car is the following:
New EGR valve
New Vacuum modulator
New Brake Booster
New Master Cylinder
New Wheel Cylinders
New Brake Pads
All brake lines and vacuum hoses have been checked and in great shape.
The battery and Alternator are also in good shape.

I am at a loss as to what the next step should be. Any help would be appreciated.