I got the new sensors today and have installed them. While under there I found the left post cat sensor was not plugged in. I will see if it is better now.

 

So much for throwing codes based on performance if its not even reporting that the sensor is not plugged in. Try unplugging them all and see if you get a code.

 

After my last post I talked to my friend who stopped by the night I had the truck in the garage. He made a comment about unplugging it as a joke. Pretty sure he did the plug was spotless inside and with the weather and roads here I am sure if I had driven it down the block with it unplugged you'd be able to tell. That would also explain why no code was thrown. He's a funny guy!!

 

i have had o2 sensor get "lazy" where they were slow to respond... granted it was an obd1 setup but still could happen to any o2 sensor. The failure mode was pinging when temps warmed up. If your able to monitor IATs I will bet the cold is also contributing to poor mpg. Its been a while since I had a gasser but I know from experience on my CTD, mpg is best at 100*f.