Have had it to a local shop 3 times, 3 of 4 calipers needlessly replaced until they told me that they think its the EBCM. Depending on how many times you hit the brake it eventually reaches a point where pedal is high and hard followed by a terrible shimmy as one of the calipers lock up. After it sits for a while the brake pressure is released and back to normal. This problem started out where it would go back to normal after just a few minutes parked, now it takes hours. Before I go throwing another pricey part in it, was hoping for other opinions. Thanks.

 

Maybe internal brake hose failure? The hose gets clogged or the internal lining ruptures causing the hose to behave like a one way valve.