Paccar PX8 Engine brake delay

Hey guys. I have a 2009 Kenworth t370 with the Paccar PX8 / Cummins ISC rated at 330/1000. It has a single stage engine/exhaust brake (off and on). Over all the engine brake works great and really pulls the truck to a halt... How ever it has a 2.5 second delay form letting off the throttle to when it engages. because of this it is relatively useless when slowing down to a stop and using the brake at the same time. I have a 10 speed Eaton and when braking and down shifting, I get the engine brake for maybe a few hundred revs before the next down shift. So unless Im just coasting and gradually slowing down, the engine brake is pointless. Is this normal for this engine? everything else ive driven, between mack, peterbilt, larger Kenworth's, and international - the longest delay ive seen was maybe a half a second but is other wise instant. Is this an issue with the VGT on the turbo? Programing issue with the computer? Or is this just how it is?

side note: the engine does have 730K miles on her and the turbo actuator is sort of wonky at times. On very very rare occasions, usually while accelerating and in between shifts, the truck will lose throttle response and act like the engine brake kicks on even though its off. This will last for about 3 - 5 seconds. If you try to gas it in this period, the truck will just slowly spew a thick cloud of black soot. After that time, she will roar back to life and all is normal. No check engine light.

 

Good to know that's a programable thing and not an actual issue. I'll swing by the kenworth dealer here this week and see if they can do that. Gotta pickup some filters anyways