ive been experiencing intermittent power loss with braking. It feels like a loss of vacuum at the brake booster. I only experience it during light and long-duration brake application (slowing for an off ramp or red light) I always feel pressure build once a specific pedal travel is reached or I reapply the brakes. Toyota master tech couldn't find anything wrong and stated it was normal for the design of the calipers once the brakes pass a certain ware point. He stated I was at about 40% all around. Advice?