Sales and profit lifts to Costco (COST) from surging gas prices may already be pumped into the retailer's stock price. Since the start of Operation Epic Fury on Feb. 28, Costco stock has gained 1% — outperforming the S&P 500's (^GSPC) 8.2% drop. The relative outperformance reflects investors rallying around a simple, two-part thesis on Costco. First, spiking gas prices send people to Costco for the cheapest possible gas, which in turn sends them into a Costco store for the cheapest possible groceries. ...