Greddy definitely still has a cut, it's the one that caps the signal and is adjustable via the screw that Pete mentions, and a multimeter IIRC?
All your findings sound pretty much spot on so far, the reason for the silly lean on overrun is that the injectors shut off and your engine is just pumping air. Not sure what the AEM gauges show, but my Innovate (which seems to have a much broader range) switches from Lambda to % Oxygen in the air at that point.
This is why, contrary to popular opinion, coasting down a hill in gear is much better for your fuel economy than coasting with the engine idling