GM, Ford Cut Production; U.S. Sales Fall  DETROIT (Reuters) - General Motors Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=GM.N target=/stocks/quickinfo/fullquote"&gt;GM.N&lt;/A&gt; and Ford  Motor Co. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=F.N target=/stocks/quickinfo/fullquote"&gt;F.N&lt;/A&gt; posted weaker U.S. sales for August on  Wednesday and both cut planned fourth-quarter production as  their aging vehicle lineups lost ground to rival Chrysler and  some foreign brands.