RepairPal Certified shops can diagnose and repair your 2002 Chevrolet Silverado 1500. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Up stream is referring to the oxygen sensor before the catalyst converter. I suggest you rear the article Fernando recommended,n O2 sensor will not likely fix these codes.
There is very good information on this site about those codes. I searched on the Encyclopedia and found http://repairpal.com/OBD-II-Code-P0171-and-P0174 and http://repairpal.com/OBD-II-Code-P0442