Catalytic converter setup with true duals

[LostX]

I am trying to get my exhaust setup properly and some weird stuff is going on after the previous owner converted it to true duals.

If I look under the truck there are 3 Catalytic converters, 1 on the drivers side and 2 on the passenger side.

I assume on the original exhaust the 1 extra cat came after a ypipe, I might be mistaken.

I just want to get my 02 sensors set up properly to get the motor running at its prime.

What's the deal with 3 Catalytic converters?

(This is a texas truck with federal emissions)
(It is true duals with no crossover whatsoever)

 

[jkeaton]

Post a picture. You sure they are all catalytic converters? What year?

 

[LostX]

It's a 96 vortec 454.

 

[jkeaton]

If it's a 96, it will need a before cat and after cat O2 sensor. Doesn't matter which one, as long as there is a pre-cat and post-cat sensor.