Engine brake staying on

[Chamberpains]

If you float shift then rest your foot lightly on the clutch pedal to engage the clutch sensor when you shift. This keeps the jakes from barking in between shifts.

As for your problem, I'd wire it back to factory and see if your problem persists. We can't know what all you did to wire up you shifter switch so it needs to be completely excluded for any one on here to give ideas as to what could be happening. If the jakes operate normally other than what you describe it more than likely is gonna be in something you wired up. Maybe even your wiring might have damaged the original switching system. It's hard to tell without being able to see what all you have going on.