I've not had the (dis)pleasure of having to replace cats on an Expy (yet), but from what I've read here & other places, most folks have had better luck with OEM parts than aftermarket ones, mainly due to the way the computer detects & reacts them, like throwing codes when nothing is actually wrong and whatnot....
I'm not saying that aftermarket ones absolutely won't work ok, but there seems to be more issues with them as opposed to FoMoCo ones.....
However, I did have to replace the factory one on my son's '09 Impala at around 200K miles (it started throwing several codes & having some performance issues), and my trusted mechanic gave me 2 prices, as well as the pros/cons of each option:
1) Aftermarket = $388 installed, with a 90 day warranty,
OR
2) GM/OEM = $893 installed, with a lifetime warranty......
Guess which one I went with
That was almost 2 years ago, nevernottaproblemo !
