I have a 1998 K2500 with the 7.4. It is a hydroboost truck. recently ive noticed, well hard not to notice. At slow speeds less than 10 MPH the brake pedal gets real stiff(You can push through it) and there is a humming noise from the engine bay. Its not a PS whine, its a much different sound. it does get worse if you turn the steering wheel. It leads me to believe that the hydroboost or PS system is failing. Any input would be appreciated.