Ready for the verdict?
My APA has been kegged for a few days now, and I can confidently say that the off flavor is GONE! Really, the only thing I changed for this last brew was to boil water in the kettle for an hour to replace the oxide layer. Actually, I boiled water for an hour, then cleaned the inside of the kettle with soapy water, rinsed, then boiled again and left it. There was definitely a hazy gray layer around the inside of the kettle and I didn't touch it before brewing.
I owe a big debt of gratitude to everyone who posted suggestions, especially insanim8ter and thadass. You guys were the ones who figured out that I removed the oxide layer on my aluminum pot. PSA to all of you who use aluminum kettles. It does a fine job, but do NOT clean with oxy-clean. If you do, then you really need to heat it or boil it.