I own a BMW X-5, 4.4 ltr V-8. I am having a issue with my brakes, they lock up

What is your question?

I own a BMW X-5, 4.4 ltr V-8. I am having a issue with my brakes, they lock up after I've been driving a while. Over the past 2 months I've replaced the brake booster, abs module, vaccum hose and both rotors on the rear of the vehicle. I've taking my car to several BMW dealers who can't find out whats wrong. The problem started 2 months ago, my brake pedal was hard to push in when i was driving, then the 4x4/DSC, brake lights showed inactive status. While the lights were on, the car started to slow down without me pusihing the brakes. Eventually I damged the rear rotors, so I replaced them and took the vehicle in. The BMW tech stated that he believes it was the power brake booster or the ABS module. We'll I am currently tired of spending money and my car is still doing the same thing.