the 02s should read somewhere around 890mv at wot if you scan it...

 

It would be interesting to know what goes into a Chev. LS9 or Caddy LSA catalytic converter to allow them to live under extended WOT usage.

The right LS9 cat is $762 and the left hand cat is $761.
LS7 right hand cat is $541 left is $622.
LS3 right hand is $442, left is also $442.

peace
Hog

 

Good chance the problem is magnaflow cats jus plain dont perform as good as the stockers and the rear o2's are picking up on it.Mind you this is from a emissions stand point.I had the same problem with my camaro when switching to high flow cats.There is a couple ways around it you might be able to tune the problem out,delete the codes in the tune using efilive,or add some fittings to get the rear o2's out of the exhaust stream.I have used all of the ideas above to cure this problem on various vehicles.