See also:

Customer Assistance Offices (U.S. and Canada)
GMC encourages customers to call the toll-free number for assistance. However, if a customer wishes to write or e-mail GMC, the letter should be addressed to: United States GMC Customer Assistance ...

Cellular Phone Usage
Cellular phone usage can cause interference with the vehicle's radio. ...

Trailer Gain Adjustment Procedure
Trailer Gain should be set for a specific trailering condition and must be adjusted any time vehicle loading, trailer loading, or road surface conditions change. Setting the Trailer Gain properly is ...