Have you tracked down the problem yet? Did you pick up a multimeter to test the resistance values as suggested?

Just to bring some closure to this thread guys. Well I finally had a chance to drive it to my trusty mechanic down in Tennessee. We checked the relays and the continuity on every single wire to and from the dme. Everything checked out, so we decided to check the 02 sensors again. I supposedly had all four replaced several months back. I noticed the post cat driver side sensor looked older, just because the wiring was dirtier. We decided to take it out and check it. The sensor was destroyed! It was surely original and was even melted. My mechanic told me it was hands down the worst he had ever seen in his 30 years. I guess the shop forgot about that one!? So we got an o2 sensor and slapped it in. The car runs great now and averaged almost 30 mpg on my drive back home last night. Over 500 miles now after replacing it and no CEL!!!! Obviously not ALL 4 of mine were replaced and made this a headache to track down. Moral of the story is if you're replacing one o2 sensor, replace them all. Thanks again for all of the suggestions and hopefully this will help someone.

I doubt
 

that all 4 were ever bad and you usually replace them individually or maybe as a pair nearest the engine and almost never should you need to do all 4. Not sure I've ever seen codes for all 4 simultaneously thrown except for some problem upstream.

But sure glad for you your sage seems to be over...