OK.. I need to tap the collective here.. I'm stumped. 07 Yukon. Vacuum boosted brakes.

Last week was coming to a stop and the pedal went to the floor like I blew a line. No lights, no external leaks. Pumped a few times and it came back like a normal pedal. The problem is intermittent. Brakes will be fine for a while (a few miles) and then all of a sudden I lose the pedal and have to pump it up..

Tested the master and it was leaking internally, so I replaced it.

Now the pedal is a little stiffer, but still drops out every so often. Tested the boosted and found the check valve was leaking down, so I replaced it.

Again, pedal feels better and drops out less often, but still intermittently. Been a few years since I did brakes. Maybe the rotors are warped and causing the calipers to back off? Don't have a pulse in the pedal, but what they hey? Let's put pads and rotors on it.

Now the stupid thing stops better than ever, but the pedal still goes to the floor and needs to be pumped up every so often. I'm stumped. It acts like it's bleeding down hydraulic pressure, but I can't think of anything in the system that could cause that without an external leak somewhere..

Any ideas?

Update: replaced both front wheel bearings today. Problem still exists. I have also determined that the problem only exists after a right hand turn. I'm stumped.