One problem related to suspension has been reported for the 2004 GMC Sierra. The most recently reported issues are listed below.
The contact stated the front brake lines were rubbing against the caliper, causing a hole/loss of fluid, and failure in the brakes. The vehicle was taken to a dealership, where they replaced the brake line, and placed a rubber boot where the wearing occurred. The dealership said defect was a result of the suspension modification to the vehicle. The contact took the vehicle to another mechanic, who stated the rubber boot would not stop the wearing, and the modification could not have caused the problem.