see if autozone can watch it on the scan tool, to watch it cycle. you might be able to do a bench test but i cant think of how right now. i can look this weekend in my manual. but i always run the truck and just watch it switch from rich to lean mode on the scan tool.
MP- i thought it was an o2 sensor, i just couldnt figure what the ego was.. i was thinking heated o2.. ive never heard it called that before.