Q: Overdrive on or off?

Unfortunately, this question requires additional information as to the make and model of your vehicle to properly answer. There numerous vehicles on the market with varying overdrive designs that operate mechanically different. In general, most overdrive transmissions will be programmed to push the transmission into the highest gear possible when the overdrive function is on in an effort to increase fuel economy. When you turn the overdrive function off, this causes the power train control module to prohibit the transmission from engaging the last (or highest) gear. By default, this causes the engine RPM to remain at a much higher level, thereby creating much more torque and power. The result is much more acceleration power.