ok...im stupid when it comes to trucks...ive only had my liscense for a year in june...and im ignorant. But i want to learn and ive learned alot from here. So here is my attempt to learn some more. I had a 83 chevy scottsdale that didnt have overdrive...thing had D-3-2-1....my 86 k5 has OD-d-2-1...someone explain the difference....should i drive in D and use overdrive only on highways? is one better on gas? help here.