If you have two O2 Sensors then you have a pre-cat between them which is part of exhaust manifold. The main EGR-to-manifold tube comes from rad side around to firewall side and EGR valve, small pipes with hoses then go to back pressure transducer (DPFE).
Main cat is the one under the floor console and I suspect that's the one that was previuosly replaced.
Is your CEL (Check Engine light) on and if so have you retrieved the code?
p.s. Good to list your location.
