Investors might want to bet on Costco (COST) , as it has been recently upgraded to a Zacks Rank #2 (Buy). An upward trend in earnings estimates -- one of the most powerful forces impacting stock prices -- has triggered this rating change. The Zacks rating relies solely on a company's changing earnings picture. It tracks EPS estimates for the current and following years from the sell-side analysts covering the stock through a consensus measure -- the Zacks Consensus Estimate. The power of a changing earnings ...