Driver side low beam head light losing contact

The terminal is likely corroded. Sometimes simply unplugging the connector repeatedly will scratch a clean spot that will make good contact for a while. You can also remove the bulb, then sand its terminals with fine sandpaper. If you do that, it is important to not touch the glass with your fingers. The intense heat from the bulb will cause the fingerprint grease to burn through the glass and ruin the bulb. Hold the bulb with a clean, oil-free rag.

If the terminal in the plug is badly corroded, you can replace that entire plug, or you can visit the GM dealer's parts department. They should have replacement terminals.