VNL 760 exhaust brake always on

Hi my exhaust brake on my 2020 vnl is activating as soon as my air drier pops off, I replaced the main valve that I think controls the air flow (near the oil pan and close to the fan in front and on the driver side, don’t know part number but it was about $900) and we put in a new compound turbo unit but the exhaust brake still does the same thing, what do you think it might be I have a great understanding of the engine breaking system, however this is the exhaust brake. The new compound turbo systems also use an air activated piston mounted on the diffuser after the second turbo and headed to the exhaust system. The compound turbo is mounted directly to the cam gears so the only way to slow it down is to cut the exhaust and increase the pressure to slow down the turbo rpm’s and in turn the trucks cams and crank will slow down. Inside the truck I do not have the engine or exhaust brake activated, activating them does nothing and when I press the accelerator that piston mounted on the diffuser opens up and there is no more increased exhaust back pressure or exhaust brake. I found the main air supply for that piston and disconnected it and the back pressure issue stopped as if I was pressing the accelerator. But I can’t let the truck drive like that. What do you think it might be?


I have not tried to replace the main valve that supplies the air. This valve is very close to the air drier, picture attached