Hello.

Yes, you are right. Disconnect the cat on that bank.

Then if that is not the problem, check your cylinder compression to check for base engine problems. Check engine vacuum. These valves can stick, pushrods can bend.

Also, carbon on the valves has been quite common. You can use top end engine cleaner to flood the engine. Keep cranking while spraying the cleanet into the throttle body. Let sit overnight. Then, crank the engine at wide open throttle untill it starts.

Check for injector pulse. You can do that with a noid light.

Check your coil trigger. This should be done with a scope.

Let me know what you find.

Yes, At this point I would surely check for clogged converter(s). It is best to remove the o2 sensors and insert a gauge and test backpressure. But, you can remove the o2 and look for a noticable power increase. Or, like you said you can disconnect the exhaust.

Unless the truck is a flex fuel vehicle it should NEVER be run on ethanol.

Clogged cat will cause a fuel smell.

So, no different injectors for flex fuel.

I would suspect either engine carbon or contaminants in the fuel rail.

Soak the engine intake with upper intake cleaner and let it sit overnight. Then, start it and run it at higher RPM to blow out the cleaner.

Remove the fuel rail and see what comes out. It is common for contaminants to enter the fuel rail and not pass through the fuel pressure regalator.

Remove the valve covers and inspect the rockers. I have seen rockers fall off and cause rough runs.

Let me know what you find.