1998 Ford F-150 P1151 and P0155 Fault: O2 Sensor Issues After Exhaust Work

I own a 1998 Ford F-156 with a 4.6L Triton V8 engine. The truck ran well initially, but the check engine light remained on, indicating exhaust system issues. I had the exhaust gaskets and elbows replaced at a shop, however, they improperly installed the original oxygen sensors into the new exhaust pipes. About a week later, the truck ran smoothly—until I turned it off. After about two hours, when I tried to restart it, the engine wouldn't start. Resetting the battery allowed it to start immediately. Since then, the performance has declined significantly: it sputters and runs sluggishly in drive, though it seems stable in park. The current symptoms are so severe that it barely moves due to lack of power or bogging. I've had the vehicle scanned and received codes P1151 and P0155. The original shop attempted to charge me $500 for catalytic converter replacement, which I believe is not necessary given the symptoms. I'm seeking advice on how to diagnose and fix this issue—could it be a faulty oxygen sensor or another component? Any insights would be greatly appreciated.