One problem related to automatic transmission cooler has been reported for the 2005 GMC Sierra. The most recently reported issues are listed below.
Extreme overheating of 3500 duramax while towing. Loss of power and overheating of transmission and engine. Numerous contacts with general motors and attorney general in michigan. Gm acknowledges there is a problem but don't know what the problem is therefore no fix for the problem. Are continuing to find a fix. We tow a 5th wheel in the colo. Mountains and this could lead to very serious problems if the engine should blow and we would have loss of steering and braking.