Same as above, No Fix Yet

Think its a master cylinder/servo/Vacuum Problem

Problem usually happened when pulling up to a stop but has happened on the road at normal speeds. Pressing on the brake feels normal but truck continues to roll forward with minimal or no effect. This problem is so intermittent it happens like 1-2 times a month but it is getting worse. Have been to the dealer 3 times before and they found nothing. Going back for a 4th time.