No power

We need to start with checking for codes. Here is a guide that will help with this:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Once we know if there are codes we will have a better idea.

If there are no codes then here is another guides to cross off the basic things that will cause a low or no power issue. Let's cross these off and based on if this makes a difference or not that will be info either way. No result is still a result that will help us figure this out.

https://www.2carpros.com/articles/symptoms-of-low-engine-power

Lastly, if there are no codes and these items don't make a difference the next thing would be to get a video of what this is doing. The reason is, I am thinking this could be a torque converter issue. Normally a converter will fail and the clutch will stick on and stall the engine. However, if the stator locks then you will not have any torque multiplication and it will barely accelerate. Then when you shift it to neutral it will rev up like normal.

Let us know about this info and we can go from there. Thanks

Great job. That is correct that if you removed them and the power came back then the converters are plugged. Here is a guide that will help testing this:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please run through this to confirm a converter but it sounds like you already did.

Let us know what you find. Thanks

Just to be clear, you have temperature on the passenger side of 605 and the driver is 205 at the exhaust manifold?

If that is the case then you have a misfire or raw fuel going through the exhaust.

There are a number of causes for this but because you are not mentioning a misfire, I suspect you have an injector or two sticking open that is dumping fuel.

What I would do is install the exhaust back to stock and monitor the o2 sensor data with a scan tool to find out if that bank is rich.

Below is a chart that helps with this. If that is the case then you can replace all the injectors or swap them from side to side to see if the issue switches banks. This takes a little more effort but it eliminates guessing.

If removing the exhaust causes it to run much better then that is pointing us in this direction. Now we just need to find why the exhaust is plugging.

If the o2 is not rich then we are going to have to check for a head gasket issue as you could have coolant or oil going through the exhaust as this is what normally plugs the exhaust.

https://www.2carpros.com/articles/head-gasket-blown-test

Let us know what you find with this. Thanks