[Shotimes] Needed Fresh Perspective

[DAVID PILLSBURY]

Well here is how it started. I got lazy and did not have time to change the oil ran it through a Quaker State. A few days later I light up the CE with a 41 Run the O2 sensor through the tests and they test fine. change the fuel filter it was old. 41 went away for a few days then came back with a 41 and a 91. A few hours ago the party broke up here. I had two Ford techs a Ford engineer. A GM tech two GM engineers A Chrysler Experimental engineer. I Certified Mechanic (me) Had every sensor tool known to man on this thing. And still can't find the reason the codes are comming.  Both O2 sensors check ok. So now I'm at the point where the rear is lean and the O2's are not switching.
Anyone here got anything me and the boy wonders have overlooked?  I'm open to suggestions. It's driving me nuts. I'm losing sleep over it.
Dave. SHOly going crazy