Hi my name is ***** ***** you for requesting me.
This sounds like you either have a broken jake solenoid spring or failed o-ring under jake solenoid. Depending on if you have C brakes or Jake brakes it will be the same issue.
This is a easy repair,,remove valve covers,remove jake solenoids and inspect o-rings and springs, I think you will find one broken or damaged.
I recommend changing the springs and square cut o-rings on all three solenoids, they come in a KIT.
Depending on what engine and jake you have this will give you a idea of what comes with kit click here
You can also just replace failed part but you won't know what you need until you get apart.
Jake solenoid or C brake solenoid they will look about the same click here
I have a wake and wedding later today so I won't be around much today, if you run into any trouble let me know I'm happy to assist.