GM Cutting 900 Jobs at Michigan Plant  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; will cut  about 900 jobs early next year at a pickup truck plant in  Pontiac, Michigan, in a move underscoring sagging demand for  some of its most profitable vehicles.