X15 chuffing through air cleaners at low rpm on jake brake

[Jakt2016]

They sent me a replacement. It didn't change it. I believe I have a couple of weak jakes. I just haven't had time to check them. I've been driving it a Lil different. I usually let the rpms drop out with the jakes to push it out of gear and down shift. Been doing that way for 25 yrs. So now I pull it out at about 1300 and downshift. It hasn't done it since. But I've got to pull the valve cover and check the jakes running. Thank you for your help.