Hello- I have a 97 chevy blazer. It shakes and seems to lock up the brakes a bit at higher speeds. I have replaced the front rotors and pads.

 

You might want to check out the rotors to make sure they are true. Also, check the "rubber" brake lines going to the calipers. They are known to collapse internally that will cause the brakes to lock up and and not allow the pressure to release.