Before you spend any $, take your coach to a large vacant parking lot. Put the coach in neutral with the engine running...fully stroke your brakes 10 times holding the brake pedal to the floor for 30 seconds each time.
Next, put the coach through some hard/panic type stops to remedy any brake glazing that may have occurred and to see if the step above put your automatic slack adjusters back in adjustment/calibration.
Based upon your narrative, you are very easy on the brakes (can cause glazing) and have not calibrated your slacks (should be done regularly).
Let us know if this helps.