Mechanical Parking Brake problems of the 2001 Chevrolet Blazer

The parking brake on my 2001 Blazer does not work when the vehicle is parked "nose-up" on an incline. (vehicle has rear disc brakes with a small drum/shoe parking brake. ) the dealer told me there is nothing wrong with the parking brake, I. E. It is not suppossed to hold the vehicle in this position, parking brake will only hold the vehicle in the "nose-down" position on an incline. The dealer told me it would be a waste of money to have them disassemble and inspect the parking brake components. Gm customer service refused to provide a clear answer to my inquiries and keeps refering me back to the dealer. Gm customer service refuses to communicate with me further on this issue. Gm customer service refuses to put their prior responses and refusals in writing, on letterhead. In short, gm knows this is a dangerous design defect that will cost them a lot of money to correct.