One problem related to high/low beam switch has been reported for the 2005 GMC Envoy. The most recently reported issues are listed below.
The contact owns a 2005 GMC Envoy. While driving the vehicle approximately 30 mph the high beams began to blink when the contact removed the foot from the accelerator pedal. The contact was driving behind a police officer, and when attempting to decelerate, the high beams started blinking. The officer stopped him and stated that it was a safety problem. The contact took the vehicle to dealer for repair, but was unable to perform repairs. After the vehicle left the shop the failure occurred at 50 mph. The mechanic performed a diagnostic, and found no failures. The GMC technical support representative stated that they were aware of the failure, but did not know how to perform the repairs. The current mileage is 37,000 and failure mileage was 1,000.