Always a code

I keep getting a variety of code but all at different times.
Codes started with low cat signal. I have replaced the cats and all 4 O2 sensors. Sensor tested first, all within spec.
I entered up having to put spark plug no foul adapters on the O2 sensors to stop the codes. Still get a code once in a great while.
Then on occasion I get the po669 bad ECM code. I clear it and it goes away then I get the evap system code. Changed the gas cap and we will see if that goes away.
Are the cats issues common on these xrunners? The truck always runs great even when the codes come up. I'm just sick of the codes. Are these 4.0 computers just a pile of crap or what? Is there a fix. Have not found any failed parts so far.

 

How many miles on the truck? Still have stock headers or have they been switched to something aftermarket? Any tuning done on the ECU or still stock?

 

No P0669 in the FSM that I can find?
Maybe it's a generic code on your scanner?

 

Truck is a 5 lug x runner 4 door extended cab. With 151k miles, K&N intake air system, and Flow Master muffler. 6 speed manual trans. 33 in tires.