Jake Brake Issue on DD15

Hey hope all is well. One of my trucks were bypassed in the past and drivers been complaining about his brakes so finally I took it for a test drive and discovered that engine brake is always engaged even at standstill if you hit the throttle you can hear the engine brake cutting the rpm’s drop quick even between shifts at low speed. This only happens when the engine warms up, when it’s cold everything’s perfect and obviously when you turn the engine brake off from the steering wheel I’m not sure if this is something related to the calibration in bypass or solenoids acting up. The calibration was fine it never had issues for the past 400k miles, anyone have any insight on this?