Bloomberg: The U.S. Postal Service purchased more than 30,000 ethanol-capable trucks and minivans from 1999 to 2005, making it the biggest American buyer of alternative-fuel vehicles. Gasoline consumption jumped by more than 1.5 million gallons as a result. The trucks, derived from Ford Motor Co.’s Explorer sport- utility vehicle, had bigger engines than Jeeps from the former Chrysler Corp. they replaced. A Postal Service study found the new vehicles got as much as 29 percent fewer miles to the …