The only thing I can offer is that I have a good (passed smog recently) cat that your welcome to borrow. I'm in Santa Clarita.

my bad................AIRFLOW SENSOR. gizmo = flap. mine was aside from dirty, not doing what its supposed to do. yeah everything i listed was a long way to figuring it out, but everything is new and it runs perfect! and i have spares LOL! good luck.

remember one thing...........since everything that is done smog wise in calif. sooner or later lands on our doorstep here in arizona, maricopa and pima counties(phx and tuc) are very strict on all parts being in place. if they even suspect tampering with cat, you will have big fun for sure. by starting with a stock cat that works you have a baseline to work from. wish i had this info when my problems started rearing their heads. DME seems to be catch all problem solver, well it wasnt that nor the CHT, nor the O2, and on and on. i passed emissions with stock oem cat, then put exhaust and bypass on. then things started going downhill as far as replacing items to cure problem.

Why not have your mixture adjusted to spec and then have a pretest?

More cost effective than replacing good parts you don't even need.

Joe