To find the correct torque specification, you MUST consult a repair manual specific to your 2003 Chevy Impala. These manuals are available online (often as PDFs) from various sources, or you can purchase a physical copy from an auto parts store. The manual will provide detailed specifications and instructions for your vehicle's make, model, and year.
Using an incorrect torque specification can lead to serious safety issues, including wheel detachment and accidents. Do not attempt this repair without the correct information.