DETROIT, Mich (WLMI)  Fleet purchases are being credited for helping General Motors' domestic sales rise seven-point-six percent in July.  GMC sales jumped more than 36-percent, while Cadillac sales fell 25-point-five percent.  Ford Motor Company's domestic sales in July rose by nine-percent, led by a 40-percent sales increase for Lincoln.  Chrysler Group reported its best July U.S. sales since 2007 with its figures rising 20-percent.  For Chrysler, July was the 16th straight month of year-over-year sales gains.