I have an 02 GU3 3ltr DI.
When it starts up overdrive is automatically engaged (nothing showing on the dash) and because of this I have just always driven that way.
I have turned it off on occasion when climbing hills while offroad.
This past weekend I drove over 800 kms and 200 were up and down long hills on a regular basis. I turned the OD off and the Trol just seemed happier. Fuel economy didn't suffer (haven't done the refill yet) but performance was stronger. I did turn it back on for the long straight flat sections.
So I thought I would ask how other 3.0 DI owners drive around generally.