I had the breaks on my car worked on by an AST certified mechanic the break pedal is hard it stop but it doesn't feel right i have ABS break it almost as if there is something else wrong. What could be the problem?

 

I have had a vacuum booster fail on a 2002 LW300. Stiff pedal, no noise since the booster is mounted differently than most American cars. It does not vent under the dash it is further away under the hood. This is a European GM designed car.

 

Take it back to the clown that worked on it and have HIM drive it .