ISX CM2250 engine brake help

[Johnh62]

Good morning. I'm a new member here and have a couple questions on an ISX15 engine brake. I'm an independent shop owner and have fairly significant experience with ISX engines, though I'll be the first to admit that I don't know everything!

We have a truck in the shop for a regular customer that there's no perceptible change in engine brake performance between settings 2 and 3(medium and high). All 3 switch positions are indicating normally on Insite. When monitoring VGT desired and actual I'm seeing no immediate change when setting 3 is selected vs 2.

Operationally the engine is running normally with no VGT or EBP codes or symptoms. We are stumped and haven't run across this one in the past. I appreciate any help or guidance I can get!