One problem related to tank mounting has been reported for the 1999 Chevrolet Silverado 1500. The most recently reported issues are listed below.
Brake line blew out due to corrosion when pulling to a stop light, was able to stop the truck w/o incident. This was 8aug09. Repaired on 12aug09. On 5aug11 went to replace shocks thinking they were shot, problem discovered, entire shock mount rail assembly had rusted away from the frame and is hanging in the air. Mileage: 148876. On 30sep11 gas tank dropped to the ground due to corrosion of frame, and also exhaust system components have rotted away from the frame and now hanging, there are also some cracks in the frame, mileage 149476. There is no rust or damage to the body on this truck at all. It still looks like a new truck. The frame is rotting away from under the truck. I should have bought a Ford. Will never buy another chevy. From what I see, this is a known problem that gm know's all about and refuses to do anything about all these trucks. Gm should recall and replace everyones frames on trucks like mine that have perfect bodies before someone gets killed.