Could maybe be a problem with the O2 sensor, if you have a little exhaust leak you may be getting false readings to one of you O2's... Just a guess but if you have access to a scan tool (or a DVOM meter) it would be easy to tell.

-Jeff-

1998 Black SVT Morette Twin headlight conversion Street flight turbo kit collecting dust! Rebuilding my 3.0L check it out