By ALEX VEIGA, AP Business Writer U.S. stock indexes are losing ground in afternoon trading Tuesday, on pace for a downbeat finish for Wall Street as it closes out another milestone-shattering year of gains. The S&P 500 gave up an early gain and was down 0.6%. The benchmark index is coming off back-to-back declines of more than 1%. The Dow Jones Industrial Average was down 113 points, or 0.3%, as of 2:04 p.m.