Question about Jake brakes on a cm2250

[ahrenbenjudah]

Hey guys, I'm back with another one.

One of our trucks (2013 KW T800 with an isx15 cm2250) recently had a new reman head from cummins installed at our southern shop. The driver immediately noticed that his Jakes weren't as good as they were before. He claims that going down a 5% grade at 270k lbs he used to be able to hold it in 4th with the occasional brake touch.

Now, the truck won't hold him even in 2nd on the same run with the same load.

Our southern shop brought the truck back in and opened it up and confirmed that the exhaust brakes were within tolerance. They adjusted one, and sent it back out. My driver brought it back up north and lived with it for a bit and then started complaining again.

I went with him for a drive and noticed that it was vibrating more than it should but its hard for me to gauge whether or not they're working from the butt dyno way of looking at things because I'm a mechanic, not a driver. I brought the truck in and checked the resistance on the solenoids and they were in spec, but barely.

Last Friday, I pulled the cover off and put new solenoids in, found one had a slightly torn o-ring. I went ahead and replaced the harness since they're not that pricey and its good insurance. I also threw an engine brake overhaul kit at it as well since I knew that our southern shop just swapped everything over from the old head.

After I was done, I double checked the clearances on the exhaust brake rockers and buttoned her back up. Driver told me the vibration was gone now, but the braking is the same.

Driver also stated that before the head swap, when he was on the high setting with his jake brake, his boost pressure would hit 30 psi during a sustained engine brake. Now it only hits about 20. I can't find specs on what pressure it should be hitting on a cm2250. I have read that the 870s are only about 12-15 or so. Because of this, I took a look and his turbo is working as it should, boosts to about 36-38psi on a hard pull, vgt is working as intended, everything is good on that side.

What i've done:
Confirmed the switch works.
Confirmed that the solenoids are good and working as intended.
Engine Brake overhaul kit.
New injector harness.
Oil change is less than 5k miles old and pressure is good.

So I guess my question is, what should the boost pressure be during exhaust braking, and, is it just in his head? At this point, I've almost wondered if his jakes were messed up previously and hitting too hard.