Sorry for the delay.
You got some confusing information, or something was lost in translation. Diagnostic fault codes never say a part is defective or needs to be replaced. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a sensor is referenced in a fault code, it is actually responsible for that code only about 50 percent of the time. Yours is one of the other 50 percent that is caused by wiring or connector problems. Part of the cost of having a mechanic diagnose the cause of a fault code includes inspecting the wiring and looking at sensor readings on a scanner before suspecting the sensor itself. Everything else must be ruled out first.
Do you know the number of the fault code or its exact description? There are dozens of potential codes related to oxygen sensors and they mean very different things.
Next, if the catalytic converter stops doing its job, that does not cause an oxygen sensor to set a fault code for being defective. The job of the second O2 sensor, (after the catalytic converter), is to monitor the converter's efficiency. The Engine Computer knows the converter isn't working by the readings from that downstream O2 sensor, so it would be pointless to cause the sensor to read as defective. Here again, I need to know the exact fault code number.
I'm not familiar with any heat-related tests for the catalytic converter. The fact that it is hot indicates it's burning fuel vapors. Many converters have multiple stages, or "beds", and each one cleans up something different, so it wouldn't be surprising to find different temperatures in different areas.
This may or may not apply here, but understand that when the Check Engine light was on "for a while", two things can happen. First, a second, totally unrelated problem can pop up and be detected, and if it sets a fault code that would trigger the Check Engine light, you'll never know it because that light is already on and being ignored. That second problem could be a very minor one that will turn into an expensive repair if it is ignored.
The second problem with ignoring the Check Engine light is some of the self-tests run by the Engine Computer will be suspended. In this case, the best example would be when the computer momentarily commands a too-rich and too-lean condition, then it watches for the appropriate responses from the upstream O2 sensor. When any fault code is already set for that O2 sensor, the computer knows it can't rely on its readings to be valid, so it suspends any tests that use that sensor's readings. Suspending those tests will not cause running problems, and it won't cause other fault codes to set, however, the frustrating part for mechanics and car owners is those tests will resume once the initial problem is repaired, and that's when the newer problem(s) will be detected. This can cause the Check Engine light to turn on again right after a repair is completed, and the mechanic has to start the diagnosis all over again, and he has to tell the customer there's more problems that he had no way of knowing about before.
So I can give you two things to consider. If the current fault code is the same one as you originally had, the new O2 sensor didn't solve the problem, but it's the entire circuit you have to diagnose. Second, you could have an entirely new problem that isn't related to the first one, but it went undetected until now. You said, "Car then started hesitating", but you didn't say if that was immediately when the Check Engine light first turned on or after "the check engine light had been on for a while". If the hesitation started days or weeks after the Check Engine light turned on, it is pretty likely it was caused by a second problem.
Also be aware that readings from the oxygen sensor will cause the Engine Computer to adjust the fuel / air mixture up or down by about only ten percent. That's not enough to cause a noticeable running problem. The computer may be seeing an overly-rich or lean condition that it is trying to correct, but it's the cause of that condition that needs to be diagnosed, not the readings from the O2 sensor.
Saturday, January 10th, 2015 AT 1:18 PM