Although rising gas prices in the U.S. have set off a raft of complaints this year and 60 percent of the public say they are worried about energy costs, few Americans have significantly curtailed their driving or begun shopping for fuel-efficient cars. The nation actually is on track to use almost as much gasoline as it did last year, when it consumed the highest amount ever. Americans’ appetite for gas-guzzling light trucks remains undiminished — SUVs, pickup trucks, and minivans still accounted for nearly half of all new vehicles sold in the U.S. during the first nine months of this year. There has been a small dip in the sales of the largest SUVs, but analysts say it could be because of lower stock market returns or the introduction of newer car-based SUV models rather than rising gas prices. Instead of buying less gasoline, many Americans are simply buying lower grades of gas.