Currently getting a P0420 and P0430 codes. I recently ran a O2 sensor test on OBD Fusion and iCarSoft devices. The Fusion app shows the downstream O2 sensors fail the max voltage test. (Bank 1 Sensor2 & Bank 2 sensor2) The iCarsoft shows the same failure on max voltage test. The whole system is a Magnaflow front to back. Bosch sensors were installed new. Systems is 12+ yrs old. Here is the backstory the led to this

On Fathers Day I headed to the beach w/ my daughter and doggo. I hit a massive dip in the highway on the on ramp. Tires definitely came off the ground in the front. Shortly after this the check engine light came on. Rig was running fine so chalked it up to a misfire due to the mini Dukes of Hazzard imitation. Get to the Dunes and the temps start to climb over 200. I kill the A/C but they continue to climb as high as 220. Park and enjoy the day. Headed home on the highway and go to hit the gas and I have a lack of power. I notice the truck sounds loud. Hit massive traffic and the temps start climbing all over the board. Truck sounds like someone stole my cats. I make it home and discover the Y-pipe/muffler connection has cracked. It cracked on the y-pipe connection. Found out why the temps were erratic. I head to the muffler shop and he cuts a piece of pipe in and welds the y-pipe to the muffler. Cuts off the adapter/flange hook-ups from y-pipe and muffler. Clear the code of P0420.

Fast forward to last week and while driving on the highway around 65 the check engine light comes on. Check codes and now I'm getting P0420/P0430. I have cleared these codes twice. Is it possible that I fried the downstream sensor by driving it with the cracked connection or heating it up/contaminated them and/or are my cats fried as well? Trying to figure out if this max voltage test is legit for the sensors? I downloaded the Torque App and will be trying that later today. The initial voltage reading showed fluctuations in voltage with the upstream ones and downstream at idle and warmed up. Should my downstream O2sensor voltage remain constant or fluctuate? Truck is driving normal/good acceleration and temps back to normal.

Any input/advice appreciated