When my blazer is at idle it rocks back and forth. the headers shake and the there issnt an even flow of exaust coming out the the back. the truck also doenst start up right away unless it has been runing after a while. im not getting full power and time to time it gets slugish.
Also, my break pedal wont go down to the floor and its hard to pres with barly and response of stoping.

 

It sounds like a major vacuum leak somewhere. remove and plug the vac. ports one at a time until you find the leak or if you don't find it then use a spray carb cleaner and spray around the intake and carb if it starts running better or faster than theres your leak.
A vac. leak would cause a weak fuel/air mix and cause a miss which would cause the motor shakes and a loss of vacuum to the brake booster.