Dominick Reuter/Business Insider Average gas prices above $4.50 a gallon are prompting more drivers to fill up at warehouse clubs like Costco. The company saw a 3% boost in comparable fuel sales last month. Increased traffic at the pump can also draw customers into the store, where sales are up. A rising tide may lift all boats, but rising gas prices only lift a few. Costco is increasingly looking like a winner during this round of high fuel costs as US consumers look for ways to balance their