Ahm, no, no need to work anything on the intake.
The Exhaust Brake is after the Turbo in the downpipe.
Check Google for some pictures how that would look like to find it, also you should have a switch for 8t inside the cab.
P0477 is an exhaust brake code.
By the way, K&N we don't want to see in an engine bay of a Cummins equipped vehicle as these filters are to coarse and dust out the engine - maximum possible damage occurs.
What else has been modified on that Truck?