Thanks for the replies,
The IMG was replaced a year and a half ago. There are none of the original signs of the leaaking gasket (surging, wierd idle, etc).
Last night I went out for a drive and <img src="/forums/images/graemlins/confused.gif" alt="" />the CEL was gone. I think I will try to switch the O2 sensors to see if that changes the codes.
BTW the auto parts store Checkers lists 2 options for the 2 front o2 sensors ($54.99 and $79.99) and only one option for the rear($79.99 IIRC) all made by bosch. Are all 4 o2 sensors the same or are the rear two different?
As far as the fuel filter causing the problem, I've read that a sluggish fuel filter may allow enough fuel to properly run the vehicle at normal operating conditions, However problems may show up in extreme conditions such as flooring down the Highway with the ac blaring on a 100+ deg day trying to make it to an event on time (I do not deny or confirm that I was in fact "speeding" officer....)