P0420 - CATALYST 1/1 EFFICIENCY
The "1/1" refers to Bank 1 Sensor 1. Bank 1 is where the Number 1 cylinder is located. Sensor 1 is the O2 sensor that is located before or upstream of the catalytic converter. For the Dodge Charger 3.5L engine Bank 1 (cyl 1) is on the passenger side.
So when you say you "already replaced the catalytic converter on my driver side and bank 1 o2 sensors" you still have the Bank 1 catalytic converter that could be causing the P0420 code.
The transmission limp mode problem is a separate issue from the catalytic converter.
P2767 - INPUT SPEED SENSOR 2 CIRCUIT NO SIGNAL
If the Input Speed Sensor 2 signal is equal to 0 RPM.
P2784 - INPUT SPEED SENSOR 1/2 CORRELATION
If the speed difference between the Input Speed Sensors 1 and 2 is greater than 150 RPM.
P2784 is probably getting set because of P2767. The speed difference between Input Speed Sensors 1 and 2 is going to be greater than 150 RPM if Input Speed Sensor 2 signal is equal to 0 RPM.
It's not unusual for the car to go into limp mode and then post the DTC (diagnostic trouble code). First priority for the car's computer software is to protect the engine/transmission (go into limp mode) and then post the reason for the limp mode operation (post the DTC).