TOKYO, March 30 (Reuters) - General Motors Corp. plans to sell most of its 7.9 percent stake in Isuzu Motors Ltd. , and Mitsubishi Corp. and Itochu Corp. may buy the holdings, the Nihon Keizai business daily said on Thursday. The struggling U.S. auto giant has told the Japanese truck maker of its intention to sell, the newspaper said. GM holds about 90 million shares in Isuzu, worth some 38 billion yen ($320 million) based on Isuzu's closing price on Wednesday.