Left rear locks up when brakes are applied with any real force, stays locked for a few minutes then goes back to normal (so far). Did a brake job and replaced the brake line and caliper, no change. Pedal good initially but pulses and gradually sinks if you hold pressure. No ABS light coming on so I assume no codes? Saw RABS valve was a problem on other year models, but not located on frame rail.... Lines from master cylinder go to a big block in front of left front wheel well in engine compartment, then out and along frame rails..... I don't see anything else that looks like a metering/pro portioning valve, am I missing something or is that it? Help!