There are two things I would do before I replaced any cats:
1. TB cleaning.
2. Change out the plugs for some Autolite APP764 double plats.
Do each one & then reset your computer.
I can't say for sure if these will cure it, but they will CERTAINLY give you a more complete combustion and optimize the function of your existing cats.
TB cleaning can be done in a hour or so, & is relatively easy for the do-it-yourself novice. Total cost about $3 for some TB cleaner. Don't use regular carb cleaner, get TB cleaner.
Sample cleaning Spark plugs will cost you about $4 each. You know how those are installed now.
If this fails, Buckshotmotorsports.com offers "optimized" manifolds for about $80 a pair that some happy CEGers might help you install - MIL eliminators & all.
