Hi all its been a while since i have been on here but i will get to the point...tuesday evening i was driving home from work in my 1997 Z71 with a 5.7 and when i went to stop my brake pedal got real hard (kinda like a truck w/o power brakes) and my rpms died way down to about 400 rpm almost stalling but when i let up on the brake pedal it was fine again...i am wondering brake booster or master cylinder ??? and i know these trucks are bad about intake leaks would this affect the brakes like this....the truck runs perfect until you mash the brake pedal the it acts like it sucks the vacuum out of the motor and tries to stall....also if you keep the pedal pushed it will hiss loudly like air is leaking down by the pedal (i am used to the hiss when you first push the pedal but this dont quit until you release it) it really acts like a vacuum leak or something simular...i pulled the check valve out of the booster and it is getting great vacuum there sorry so long just tring to get everything out here thanks for any help Jason