Banks Speedbrake on a Duramax

I had one on my 08 it worked great holding speed while towing down hill. I had the switch on mine with the 3 settings, along with the foot brake activation. I ran it in Medium setting while towing my 10K plus Jayco, never a problem it always made me feel confident and under control. The Onstar will not give diagnostic reports with the Speedbrake installed, I didn't care about that. I think it is a very good product, I highly recommend it.