Could really use some expert help here. I cannot do a panic stop even if i stand on the pedal. If i come to a controlled (slow) stop they seem ok. So far i've replaced the rotors and pads, the power booster and checked the rear brakes. It feels like maybe just the rear brakes are working? The problem was there before i changed out the rotors, the old ones were warped so they got swapped out. Thanks in advance for your input

If only the rear brakes were working you would know it big time. The rears probably only do 20% of the work under hard braking in a stock Blazer. Have you looked into the master cylinder being bad? Are you sure there is no air in the line?

replace mc prob solved had the some prob myself

also make sure the rear brakes are adjusted properly and bleed the system

In another truck I had a similar problem. It turned out to be a vacum leak. But it is probably a master cylider problem.

Thanks for the help. Will be putting a new MC in tomorrow, I' lett you know the outcome.