Thanks very much for the response. This makes sense. Yes, the front A/F sensor was replaced with a Toyota sensor. I just wasn't sure that if, since it was replaced 80K miles ago, that I might need a new one now anyway. Eliminating that as a variable leaves me with just the CAT as the issue, do you agree? Surprisingly, my gas efficiency seems to be about the same as it normally is.

1999 SR5 V6 4WD
Addcos, Bilsteins, Detroit Truetrac, Amsoil, etc...