First, why did you take the vehicle in? What were the symptoms that lead this "mechanic" to believe that ALL injectors needed to be replaced.
Also, BEFORE having or doing the work, ask your dealer if your vehicle is still covered by this warranty:
Campaign - Fuel Injector Replacement/Warr. Extension
Bulletin No.: 04039C
Date: December 08, 2009
Subject: 04039C - Special Policy Adjustment - Injector - Replace
2001-2004 Chevrolet Silverado
2001-2004 GMC Sierra
2004 Chevrolet Kodiak
2004 GMC TopKick
Equipped with 6.6L Duramax Diesel (RPO LB7 - VIN Code 1) Engine
Technical Service Bulletins 03-06-04-036B and 04-06-04-007I have been incorporated into this bulletin. Please discard all copies of bulletin 04039B, issued November 2007.
Some customers of 2001-04 model year Chevrolet Silverado; GMC Sierra; 2003 Chevrolet Kodiak and GMC TopKick vehicles, equipped with a 6.6L Duramax Diesel (RPO LB7 - VIN Code 1) engine, may experience vehicle service engine soon (SES) light illumination, low engine power, hard start, and/or fuel in crankcase, requiring injector replacement, as a result of high fuel return rates due to fuel injector body cracks, ball seat erosion, or high pressure seal extrusion.
Special Policy Adjustment
This special policy covers the condition described above for a period of 7 years or 200,000 miles (320,000 km), whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership. The repairs will be made at no charge to the customer.
For 2003 vehicles covered by Vehicle Service Contracts, all eligible claims with repair orders on or after October 10, 2006 are covered by this special policy and must be submitted using the labor operation codes provided with this bulletin. Claims with repair orders prior to October 10, 2006 must be submitted to the Service Contract provider.