Carl's Jr., best known for its burgers, is adding a charbroiled sirloin steak sandwich to its menu. The upscale sandwich will be sold for $3.99, about 75 cents more than the chain's most expensive cheeseburger. The new sandwich is part of the Anaheim-based chain's ongoing bid to increase the average customer bill, a move that could help the chain bolster profits in the hotly competitive fast-food industry. But when McDonald's Corp. tried a similar strategy with its Arch Deluxe, it failed badly. Carl's Jr., which has been successfully repositioning itself as a higher-priced alternative in a nation awash with burger joints, will advertise the new sandwich in English and Spanish-language ads starting Nov. 30.