Two big Asian automakers are laying siege to Detroit's most reliable moneymaker, the full-size pickup truck. According to the Pittsburg Post-Gazette, the prospects are good that Toyota Motor Corp. and Nissan Motor Co. will capture an audience with their latest pickup models, a move that could pose a serious threat to the U.S. auto industry's bottom line. Toyota announced last week that San Antonio was to be the site of its sixth North American assembly plant, dedicated to building 150,000 Tundra pickups starting in 2006. By placing its pickup plant in the Old West, Toyota is seeking to connect its product to the area's rugged lifestyle image, according to Post-Gazette. For both Japanese automakers, designing full-size pickups and selling them in volume is the culmination of a long trek to become full-line producers like General Motors, Ford and DaimlerChrysler AG's Chrysler unit. Fuel-efficient compacts came first, then sedans, luxury models, minivans and SUVs, the Post-Gazette said.