If your truck has 220,000 miles on it with the original 02 sensor, then its bad. Its recommended that the 02 sensor be replaced every 60,000 - 70,000 miles, so your way past due. An 02 sensor can go bad in two ways, it can fail and throw a code, or with lots of miles on it, it gets lazy and can`t function as it should when it was new.
A bad 02 sensor will effect how your truck runs, and your gas mileage. It would be a good idea to replace your 02 sensor. Don`t use a Bosch 02 sensor in your truck, they don`t work well in our trucks. Use a Denso or NTK 02 sensor. I got my 02 sensors from rock auto for a good price.