First off Anti-Lock Brakes in a Dakota do seem spongy however if you hear
a hiss sound that could be the Brake Vacum Booster and that must be repaired now before it goes out all the way.If it does go out you still will have brakes but the pedal will be very very hard to push down. A easy way to tell is that when the vehicle is stopped push down on the pedal and see if the engine starts to run bad.This is a sign of a vacum leak and could be the booster.Good Luck!