When Wendy's decided to remake its 42-year-old hamburger, the chain agonized over every detail. The result? Dave's Hot `N Juicy, named after late Wendy's founder Dave Thomas. The burger _ with extra cheese, a thicker beef patty, a buttered bun, and hold the mustard, among other changes _ will be served in restaurants starting Monday. Wendy's, based in Dublin, Ohio, is trying to boost lackluster sales and fight growing competition from much bigger rival McDonald's on one end and expanding fast-casual chains like Five Guys on the other. Part of the issue is that Americans are being pickier about how they spend their dining-out dollars. Another issue is that Wendy's had let its food offerings get stale over the years while its competitors continued to update their menus.