General Motors Corp. started the month by naming Bob Lutz, a key figure in Chrysler Corp.'s earlier turnaround, as vice chairman and head of product development, which Wall Street took as a sign the automaker plans to shake up its product line. But the slow economy hit all U.S. automakers hard in July, with a 7% drop in sales for the Big Three, and there are no signs that demand is perking up in August. (See related story, P. 3.) Among AdMarket 50 companies, 15 were up and 35 were down for the week.