Re: 2008 hurricane
If you're V10 is like mine, then it's peak torque occurs about 2300 RPM (60 MPH in OD). Down around 2000 RPM mine will shift out of overdrive by itself.
If you can maintain that 2300 RPM in overdrive, then I don't see a reason to shift out of it. You just don't want to be lugging down the engine, but that's not going to happen until about 2000 RPM.
You have to pay pretty close attention to this while you're driving.