I am following you now as the ecm is called a control module on that motor, I suspect you have a intermittent problem with the shift interrupt switch. Check to see if it is normally closed or normally open, Either disconnect it or jumper it to duplicate a in gear position for testing purposes. If that switch sends a in neutral signal to the module it will attempt reduce rpm and probably drop 3 cylinders
This makes the most sense to me
Hope this works out for you
Let us know
Reply With Quote