Where is the ECU on a 1999 GMC suburban 1500 5.7 4x4?

The Engine Control Unit (ECU) on a 1999 GMC Suburban 1500 with a 5.7L engine is typically located under the dashboard on the driver's side, near the steering column. You may need to remove the lower dash panel to access it. Additionally, the ECU is often mounted on or near the firewall, behind the passenger side of the engine compartment. Always consult a repair manual for specific instructions and safety precautions when working with vehicle electronics.