Toyota Motor Corp. is about to launch its most aggressive assault yet on Detroit’s profitable large pick-up franchise. But the Japanese auto giant is trying not to be too obvious about it. The bigger, more powerful Tundra is due to begin arriving in showrooms this month, and Toyota is counting on selling 200,000 by year end, and eventually, more than 300,000 annually—triple last year’s volume. With such ambitious sales goals, some dealers had hoped Toyota would roll out the new Tundra with an eye-catching base price well below competitors. But Toyota is eschewing the lower end of the market, and instead taking aim at the most-profitable, feature-loaded trucks.