This is on my 06 F-250 with the 6.0 diesel. The problem happens once a day of stop and go driving. Every once in a while when you go to hit the brakes it fells almost like the hydro boost is not working. when I press on the brake pedeal it will only go part of the way down (to just before the spot where it would start slowing down the truck) kind of vibrate for a secound or two then will go on down and fell normal. When this happens I haven't really tried to press hard on the brakes just keep a steady (normal) pressure. I'm having a hard time figureing it out, because it will only do it maybe 1 or 2 times when driving all day in town (ie.. stop and go traffic). While the pedal is kind of stuck in the hard spot, and viberating the truck is not slowing, or pulling to either side. It just stays on the same path. I replaced both front caliper, slides, and hoses, because it was just time to do it. I hoped that it would fix this problem, but it appears that it hasn't. Is there a way to test the hydro boost, or power stearing pump? I'm sure that it has something to do with one of the two, but don't want to just throw parts at it. With it being so intermiten I can't figure out a means of testing this to get to the route of the problem. Any help is welcomed.