Iac sounds like a good next culprit. Wouldent hurt to get a scantool on it and see if you have anything crazy going on like giant fuel trims or whatnot...... also my favorite test for a clogged cat is to just unbolt the downpipe and go for a drive.... if suddenly everything is ok (although a bit loud) then you know what it is. Also those 3.1s tend to blow fuel pressure regulators all the time.... so pull the vac line to it and let it idle for 10 mins and see if any raw gas comes out. If you get gas in the vac line its toasted.
