O2 sensor data question

Here is more data.....I believe the blue is downstream.

Here is another reading where I think the yellow is the downstream sensor (sensor 2)

And the graph.....

The upstream sensor usually cause the trouble while the downstream sensors report catalyst efficiency to the ecu. It must not be far out of range or the check engine light would be on. My first step in working on that vehicle is to inspect the air filter and clean the mass air flow sensor. At 75,000 miles the O2 sensors warrant replacement, but it may not fix the problem.

I've recently replaced the filter and plugs; I've cleaned the MAF; and replaced the throttle body. I replaced the TB because once I got the codes for the Throtle position sensor and actuator. But after doing all that, the issue still remains. One day it will drive fine and the next one it will have issues. I normally notice it on days below freezing. The car will start fine, drives normally for about 20 minutes, and then it starts to choke itself out when I come to a stop. I'm trying to figure out the cause.