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I am posting a follow-up to the above thread. I have found a solution to my problem and feel others may benefit from knowing what i found out. After ruling out most other possibilities, I finally replaced both O2 sensors. I kept on feeling the O2 sensor readings were the symptom, not the cause, but I was wrong. After replacing both sensors, the truck runs perfectly on all long trips (my wife drove on a 3000 mile trip the following week). My gas milage is back up to 19mpg. I have checked codes several times after long drives and I get the good ol "1 1 1" (all systems ok). Hope this helps someone who is searching the groups for answers to there similar problem.