Just an idea, but do you have any vehicle speed sensor input to the ecm? Since it's a 727 it wouldn't have a VSS on it.
If you had it in a man trans car & revved it would it have a preset rev limiter to protect against a missed shift? It would need to see the vehicle speed if it does to know the vehicle was moving & then not engage the rev limiter. It may be looking for that VSS signal.
Just a thought.