for max economy shift at a low rpm, but not so low your engine is gonna bog down and almost stall, look in the owners manual usually they have the rpm or speed you should shift at.

for max power i think a d series makes max power at 6800 rpm so around there no need to go higher.

 

It will start harming the engine as soon as it hits the redline, But even if you keep it below the redline you are still pushing the engine to as much as it could go.

 

What he said. If your that worried get an Autometer Tachometer and set the Shift-lite to 6000 RPM's. You'l never go over if you shift then. JUST DONT WAIT TO THE LIGHT COMES ON TO SHIFT. Regular driving would only need a shift every 3000 RPM's. OR, watch the tachometer on a Automatic and follow it.[sm=icon_cheers.gif]

 

ya it should say it in your manual...

BUT most the time just shift when you want to...... best to shift low and smooth. will be alot less wear on the motor and beter gas milage