By Echo Wang NEW YORK (Reuters) – The S&P 500 ended slightly higher on Tuesday as investors kept their focus on the growth trajectory of the U.S. economy, and the tech-heavy Nasdaq closed higher while the Dow slipped. U.S. stocks have been under relentless selling pressure this year, with the benchmark S&P 500 index recording its steepest first-half percentage drop since 1970, as the Federal Reserve moves away from easy-money policy by raising borrowing costs. Investors are waiting for minutes from the Fed’s meeting in June on Wednesday as they brace for another 75-basis-point rate hike at the…