Now, I was talking to a guy I know with a 91LS sedan and we got on the topic of driving on D3 or D4 and I told him I drove on D4 and he told me to drive on D3 because it saves gas. Is this true or just crap??
As far as I know D3 actually uses MORE gas... If you are traveling faster than 35 than you should allow the transmition to change to 4th gear. Higher gear = lower RPM needed and if you are traveling any significant distance you will be saving gas.
D3 is there to keep your car from shifting up. This can be helpful if you are going up and down alot of hills and the transmition continually shifts up and down, or if you are going up a steep grade and need more power. Or if you like to drive more "agressively" you might want to D3 for the more throaty intake sounds (if you have intake) and maybe even some better acceleration.