DETROIT — U.S. sales fell for all three big American automakers in June, led by a 26 percent drop at General Motors Corp. (GM), while Japan’s Toyota Motor Corp. surged. Higher gas prices, slower sales of trucks and sport utility vehicles and a lack of deep incentives compared to last summer — when GM rolled out employee-level pricing — hurt the Detroit-based automakers in a weaker U.S. auto market. The tough sales comparison comes at a time when GM’s board is under pressure to consider a three-way alliance with Renault SA and Nissan Motor Co. Ford’s June sales dropped 7 percent and DaimlerChrysler’s plunged 13 percent, underscoring the pressure on Detroit automakers at the start of a summer season they are counting on to clear an unsold inventory of 2006 models. By contrast, Toyota — now No. 3 in the U.S. market for cars and trucks — posted a 14 percent sales gain. Toyota sold more cars in June than Ford and Chrysler combined. Toyota’s share of the total U.S. vehicle market rose to 15 percent in June, up from 12 percent a year earlier. The Detroit-based companies’ market share sagged to 56 percent, down […]