ISSAQUAH, Wash. - JIM SINEGAL, the chief executive of Costco Wholesale, the nation's fifth-largest retailer, had all the enthusiasm of an 8-year-old in a candy store as he tore open the container of one of his favorite new products: granola snack mix. "You got to try this; it's delicious," he said. "And just $9.99 for 38 ounces." Some 60 feet away, inside Costco's cavernous warehouse store here in