Ebay offers Speed Daddy 99-07 Silverado Sierra 3rd Tail Brake Light for $10.95 (Reg $30.54) after code with free shipping.

Apply Code: PARTSDEALS15

Product Description:
Our LED third brake light is a quick and easy way to dress up your pickup truck. When lit, the bright LEDs (Light Emitting Diodes) are illuminated, and shine up to ten times brighter than standard light bulbs. Even when the brake is not pressed, the integrated cargo light (if equipped) gives off plenty of white light to view your gear in the truck bed. The LED third brake light has a durable Polycarbonate Lens with free form reflector, and available with either the Clear lens or custom Smoked lens.

• Plug-n-Play Operation, Low Power Consumption
• Super Bright LED Light Compare to the OE Light
• Instant On Versus Halogen Lights Ramp Up Time to Warn Drivers Faster
• Built-In Cargo Light Function
• Brings a Different Appearance to Vehicle that's Great for Show Use

Includes:

• 1 X LED High Mount Third Brake Lamp
• Hardware as Shown in the Picture Above