Thanks Jonathan, I had the same thought.

Thompson, I'm not sure. All the entries on Wiktionary or other services don't include a definition like "hell," with the most popular answers either claiming it's (chiefly British) slang for gossip (unlikely here) or an American dialectical term for spitting. A third one is a type of shrub. None of those seem particularly right.

After looking it up, it seems to have been used from at least the 1840s through the 1890s. Its usage was very widespread, even in 1840, though by 1847 it was apparently already on its way out in favor of the term "Give 'em Zack" in honor of Mexican American War here Zachary Taylor, "Old Rough and Ready" (Vermont Patriot, May 6th 1847, p. 2). Another website (click) which defines "Give em Zack" confirms that the meaning was "Give em Hell"

Given that it was often capitalized, I'd assume it came like Zachary Taylors and was named after a person made famous for their danger and/or bravery. A quick search of famous Americans named Goss yields Ephraim Goss (1806-1877), a lawyer and politician from New York. I can't definitively say if he's why it's named yet, but he's the most likely answer for me at the moment.