DETROIT -- General Motors has issued a list of fuel-saving tips to improve your vehicles' fuel efficiency by up to 25 percent. GM recommends the following to save money and the environment: * Drive 55. Each five mph driven over 60 mph is like paying an additional $0.15 per gallon for gas. * Lose the weight. An extra 100 lbs. inside a vehicle could reduce mpg by up to 2 percent, or two to four cents per gallon. * Refresh that filter. Replacing a clogged air filter can improve a car's gas mileage by as much as 10 percent or up to 22 cents per gallon. * Inflate. Gas mileage can be improved by around 3.3 percent, or seven cents per gallon, by keeping tires inflated to the proper pressure. * Re-evaluate. Research fuel-efficient vehicles. The difference between a car that gets 20 mpg and one that gets 30 mpg amounts to $550 per year (assuming 15,000 miles of driving annually and a fuel cost of $2.20). That's $2,200 extra in fuel costs in just four years.