hello and welcome to Just Answer!
It does sound like a poor connection. try to wiggle the bulb and harness and see if you can get it to act up. It may just be poor connection between the bulb and socket. Is there any corrosion (blue/white stuff) on the contacts? If there is corrosion clean the contacts with electrical contact cleaner. you can try to adjust the contacts so that they make better contact with the bulb. move the metal contacts slightly toward the center of the bulb socket. Also try some dielectric grease in the bulb socket (will help the connection). If that doesn't help you could get a new bulb socket at the local chevy dealer or at a junk yard and wire it in. hope that helps. let me know if you need more help.