The Federal Reserve's key inflation rate came in a touch hotter than expected in the second quarter, as U.S. GDP growth perked up after a slow start to the year, the Commerce Department reported Thursday. The S&P 500 tried to rally after Wednesday's sharp sell-off, but reversed lower in afternoon trade as investors weighed the implications for the rate-cut outlook. The Federal Reserve's primary inflation gauge, the core PCE (personal consumption expenditures) price index, rose at a 2.9% annual rate in Q2, above 2.7% forecasts.