The MB# is indicative of it being a factory OEM part. Our generations of trucks didn't come with a factory immobiliser/alarm. I am thinking - auto trans ECM...? It's the only other ECM that would've been fitted to a Gen 2 truck with injection. What is on the compliance/build plate in the engine bay? The trans code will tell us if it has had a full drivetrain swap at some point in it's life.