Possible $4,500 Catalytic Converter Replacement

A little background:

-2012 Jeep JK 2 door, 6 speed manual

-A couple of months ago the check engine light came on. Code P0128 and P0430. Symptoms were rough idling and decreased fuel efficiency.

-I knew what to do for P0128 but not sure about P0430. Bought new o2 sensor to replace bank 2 sensor 2 but nothing changed. Just kept driving on it as I was just so busy during this time. I never did get to fixing neither P0128 or P0430.

-Fast forward a couple of months and I am now living in Denver, CO. Instantly I notice power loss when in 1st and 2nd gear (others too, but noticeably 1st and 2nd). Sometimes I have to feather the clutch just to get up to speed! Keep in mind still experiencing rough idling and decreased fuel efficiency.

-Was told that “Welcome to Colorado! The elevation will cause loss of power until your car gets used to it and adjusts”. Well, now almost 2 months into living here still no better.

-Took it to a shop and they basically said “Yeah, you’re gonna need both new catalytic converters. Because yours are failing, its causing o2 sensors to send signals that are all over the place. That’ll be $4,500 please!”. Due to the CARB compliant requirements for the state of Colorado, you are required to get the more expensive catalytic converters in order to pass emissions and be compliant. (Thanks, California..)

-Last weekend I did a coolant flush and put in new thermostat to fix P0128. Did a cycle of Seafoam just to see if rough idling was maybe due to bad spark plugs or fuel injectors. Did a cycle of CataClean, too. Check engine light is now off (probably due to P0128 being fixed) but symptoms of rough idling, decreased fuel efficiency, and power loss are still present. I was driving up a highway in the mountains the other day and I had to downshift all the way to 3rd just to have enough “umph” to keep up with traffic.

Long story short, I’ve got a couple of problems and not sure the right answer is to drop $4.5k right off the bat to get my catalytic converters replaced without trying literally anything else to try and fix the problem.

Any advice as to other things that may be contributing to these symptoms? I haven’t gotten the spark plugs checked, but maybe I need to for the rough idle? But not sure if that is related to power loss? Keep trying more cleaners to see if that helps? I don’t know, stuck between a rock and a hard place here.