1991 Cadillac EL Dorado why is the catalytic converter stil

Engine Performance problem
1991 Cadillac El Dorado V8 Automatic 210000 miles

I had a mechanic from work tell me I needed a new Catalytic converter so I replaced it with a new one professionally installed (Meineike muffler did it). But the new converter stilll turned red. So I towed it back to my garage. I have changed the front and rear oxygen sensors, throttle position sensor, pcv valve, a tune up (replaced the rotor, ignition coil, distributor cap, spark plugs and spark plug wires). The engine starts and runs on idle for about 30 minutes, then the catalytic cnverter starts to turn red in the center of the converter. But if I drive it around the block 2 times, the converter gets red much sooner. Do I need to change the MAP sensor, or change the EGR Valve, or both? Or what else could be making my catalytic converter turn red?