It's a great name compared to peperami. As for the name, copying from a site:
"The original product was called Penn Rose--A combination of Levis' native state of Pennsylvania and his wife's name, Rose," explains Slim Jim brand director Spencer Fivelson.
But of course, Penn Rose didn't stick, and the duo decided on the name Slim Jim in order to appeal to more sophisticated bar-goers (sophistication being a more desirable trait during the 1940s, when many men walked around wearing suits and top hats). “Given that the product was more slender than the pickled sausages that were popular during this era, 'Slim' was a logical descriptor," Fivelson adds, noting that the original logo was of a man sporting a top hat and cane"