Ferrari 308 slow down light

hello,

my warning slow down light just came on for cylinders 5-8. I just had one of my cat converters replaced by the ferrari dealer 2 months ago. i dont know which converter was replaced 1-4 or 5-8. the reason i had to replace one of them was because my emissions were high and when they pulled the cats off one was good and the other ceramic honeycomb resistor was completly gone. they thought it might have got blow into my exhaust. they couldnt find the remains anywhere. do you think that is were the obstruction is and thats why the cat temp is high? with the car running the right exhaust blows hard and cool. the left side blows real week and real hot. can i take the muffler off and shake it to see if anything falls out? what is inside the muffler? can i remove the muffler and tap it on the ground sideways to see if any of the old cat resistor comes out? please help........

The 308 exhausts never had the same pressure/temp at the tail pipes so this is not a good indication.

An exhaust Gas Anylyzer is the only reliable method of starting the hunt for the problem.