Shares of Costco (COST) - Get Report were up slightly on Monday afternoon, as the discount wholesale retailer has been able to outperform recently without much profit growth, Barron's said, which is why Guggenheim analyst John Heinbockel has called this the missing piece of Costco's puzzle.

"An important piece of the puzzle, profit growth, has been missing-EBIT growth has averaged just 1% during this time due to a combination of falling gas CPG, Fx impacts, and labor/IT investments. With one-time factors abating and resurgent US comps driving expense leverage, we see EBITDA rising 9% in the 3Q, a near-term positive," Heinbockel said, Barron's noted.

Guggenheim reiterated its "neutral" rating on Costco due to concerns over valuation.

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