Engine brake troubles need some input

[Nater1977]

I am still at a loss. I have been through quick serve Multiple times. I cannot find any good pinpoint test on the diagnosis of this engine brake issue. The engine break starts feeling well about 220° and the oil temp and it gets about 30 psi on the boost. It seems like one of the cylinders is loosing compression, like one of the rockers is a letting oil by. If I could add a lot of pressure to the exhaust and then manually activate the solenoid, I could probably find the problem. But there’s no test I can see on how to do that. Any more help would be very appreciated.