Front Suspension problems of the 1999 Chevrolet K1500

Truck has a vibration in the front end at 60 to 70 mph. This vibration has been present since the truck was purchased from tom peden. The tires have been checked by firestone twice. The second trip to the dealer on 12/4/98 the service manager indicated that this was a factory defect and the new parts to correct this defect would not be available for thiry to sixty days. I requested that the vehicle be replaced or a loaner vehicle be provided since the vibration along with rough road conditions could cause a loss on control of the vehicle. The dealer and the Chevrolet refused to replace the vehicle or provide a loaner. I feel the vehicle is unsafe to drive.