There is nothing but low cat efficiency that can cause this(or P0430) code. A bad O2 sensor, or anything else will give different faults, but only low cat efficiency will cause these.
That said, there are some things that can cause cat efficiency to be low, such as over fueling(including ignition misfires and incomplete combustion) These issues will almost always give separate faults themselves, however I have seen a few times where incomplete combustion will cause the cats to not be fully efficient, before it reaches the threshold of throwing a lean code.
I would run through the tank of fuel you have in there now, and one more. Then clear the code again, and if it returns(without others as well) you're going to need a new cat.
Last time I checked, cats for these trucks were not as pricey as they are for some others(mainly the L322) but still not cheap by any means. I don't suggest going with anything that is a cut and weld in application, and as far as direct fit ones, you really do get what you pay for on this. The cheaper ones may be ceramic core, not precious metals. If nothing else, do some research before pulling the trigger on one.