Costco WholesaleCOST.O gained 1.2% after posting better-than-expected quarterly revenue and profit on Tuesday. By Ankika Biswas and Shashwat Chauhan Sept 27 (Reuters) - Wall Street's main indexes slipped in choppy trading on Wednesdayas Treasury yields rose modestly, while investors awaited developments on a U.S. funding bill and inflation data this week to gauge the Federal Reserve's monetary policy outlook. Also adding pressure was data showing orders for long-lasting U.S. manufactured goods unexpectedly rose in August and signs of business spending on equipment regaining some momentum.