From what I have read, my first thought is that your brakes may be "glazed" from frequent low pressure brake application. I have heard that several repeats of hard braking might de-glaze them. Not that I am NOT a mechanic--not even close, though I do have an Air Brake endorsement on my DL (which is mandatory for operating a vehicle with air brakes in British Columbia.) I am going by what I have read in other threads.
If no one more knowledgeable than I responds, you should ask at a truck shop.
I'm pretty sure that a 2013 vehicle would have automatic slack adjusters. To try to reset them, drive forwards then in reverse several times braking hard each time. See if that makes a difference.