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24. Do you need to shop around for better gas prices?
Sure, just don't overdo this and burn 5 gallons of gas while you search for a better price. The price difference is probably not going to be more than a few cents, so keep this in mind and use your common sense. Use your phone or the Internet instead of driving to every gas station around. Mapquest recently started "Find Gas Prices" service.

25. Do you need to use a fuel injector cleaner?
Maybe... it is definitely beneficial to your engine's well being as well as gas mileage to have your injectors clean. Just don't overdo this and add a bottle of cleaner to every tank of fuel. Do that and you pay more for the cleaner than you can possibly save on fuel, and you are cleaning something that is not dirty enough to require cleaning in the first place. A reasonable mileage interval is 10,000 to 15,000 for injector additives.

26. Should you drive in a higher gear?
Sort of... especially in a standard shift, you want to drive in the highest possible gear, without overloading your engine. Generally an engine is most efficient around the middle of its RPM range. More specifically - slightly lower than the torque peak RPM's. If you are in too high a gear your engine RPM'S will "lug" or drag down the engine. Keeping an engine speed too low (closer to idle) will overload the engine, increasing its wear and seriously hurting gas mileage. Automatics do the thinking for you, but with manual you have to develop this skill for yourself.