In this articleWMTCostco Wholesale, Sam's Club and BJ's Wholesale stores.Getty ImagesOn Costco's last earnings call, executives were grilled about a problem few companies have: how is the company managing crowded stores and jammed-up parking lots?That dilemma is a sign of the times for membership-based warehouse clubs. More Americans have literally joined the club — fueling growth for Costco, Walmart-owned Sam's Club and BJ's.All three retailers are opening more locations across the country. Shares of the c ...