Failed Emissions Test

I failed on the CO reading. Limit at cruise it 1.1 and I had 5.5. Replaced O2 sensor, plugs, air filter, PCV valve and the oil. The motor has 160K, but the second Cat has 294K. Any ideas on how to get to CO reading down?:

replace the 2nd cat. has the 1st been replaced at all?

The first Cat has about 50K on it, but the second has the full 160K.