The U.S. dollar remained firm in the upper 160 yen range early Thursday in Tokyo after climbing to its highest level in over 37 years on expectations the interest rate differential between Japan and the United States will remain wide. The dollar rose as high as 160.88 yen in New York, surpassing 160.24 yen hit on April 29, a level that likely prompted Japan to intervene by buying the yen for the U.S. currency. The euro also climbed against the yen overnight, hitting 171.79 yen, its highest level since the European currency was introduced in 1999. At 9 a.m., the dollar fetched 160.63-64 yen com…