GMC Vandura 4 speed auto box questions

[egntpilot]

Hi,
May seem like a strange question but....

I've just bought a 1990 GMC Vandura full size van. It has what the owner described as an auto box with overdrive. I've driven standard 3 speed autos which are set up with a "d" for drive and "1" and "2" .This column change however has two "d" settings, the first one after neutral is a "d" surrounded by a box, the next one is the usual "d". The van has no user manual or hand book so my question is, how do you operate this particular system? Around town do you use one of the "d" positions and the other for the open road? And if so which one? Or can you leave it in one position no matter what, and again , which one? Hope these questions aren't too dumb and someone on this board can assist

Thanks in advance for your time.

Steve

[camodiak]

pilot, the first one with the "O" is overdrive, second one "D" is just drive. i always keep mine in O/D. when i pull something and going up hilly sections of road, i will put it in "D" so it dosen't keep going back and fourth between the two. O/D on hte highway at crusing speed will better your gas mileage. hope this helps.

[egntpilot]

Many thanks,
That's exactly what I was after,

Steve