There has been a factory recall on some for that type of concern. It involves a reprogramming of the exhaust fluid system and would have to be done by the dealership.
Here is what it states.
Recall - Diesel Exhaust Fluid Calibration Enhancement
Bulletin No.: 11001A
Date: August 05, 2011
Subject: 11001A - Diesel Exhaust Fluid Calibration Enhancement
2010-2011 Chevrolet Express
2011 Chevrolet Silverado HD
2010-2011 GMC Savana
2011 GMC Sierra HD
With a 6.6L Turbo Duramax Diesel Engine (LML/LGH) Supercede:
The Service Procedure in this bulletin has been revised to include the following statement.
Note: If a customer comments about a diesel exhaust fluid (DEF) low or speed limited soon message that currently will not clear of the DEF low or speed limited soon latch message appears soon after programming the engine control module (ECM), refer to the most current version of PIP4864 in SI. Please discard all copies of bulletin 11001, issued July 2011.
General Motors has decided to conduct a Voluntary Emission Recall involving certain 2010-2011 model year Chevrolet Express, GMC Savana; 2011 model year Chevrolet Silverado HD and GMC Sierra HD vehicles equipped with a 6.6L Turbo Duramax Diesel Engine (LML/LGH). The Diesel Exhaust Fluid (DEF) injection system may not operate as intended. If this occurs the Malfunction Indicator Lamp may illuminate, a DEF system warning may be displayed in the Driver Information Center, and vehicle speed could be limited.
Dealers are to reprogram the engine control module.
Involved are certain 2010-2011 model year Chevrolet Express, GMC Savana; 2011 model year Chevrolet Silverado HD and GMC Sierra HD vehicles equipped with a 6.6L Turbo Duramax Diesel Engine (LML/LGH).