10:15 a.m. Update: The major indexes delivered robust gains at the open Thursday, spurred by a strong GDP report and some good news on the earnings front. The S&P 500 and Nasdaq both gained 0.9%. The Dow 0.7% rose and the NYSE composite 1.4%. Volume was mixed. It rose 10% on the NYSE and fell 5% on the Nasdaq compared to the same period Wednesday. Several top-rated stocks surged on better-than-expected