P0420 after changing O2 sensor

Hey all,
I recently had the p0171 code on my 2000 Tacoma, so I replaced the O2 sensor before the catalytic converters. I now have a p0420 code. I used a temperature gun to test my catalytic converters and both have failed the temperature test (when comparing the in-out temp, there should bew 100degrees or greater difference). My truck is 15 years old and is at 157,000mi. If both cats are bad, is this about right...or just bad luck? I'm not sure I can believe BOTH are bad. Thoughts?

 

Also, FYI...after changing the O2 sensor I noticed an increase in power. I haven't driven enough to notice MPGs, but the truck ran poor before changing the sensor.