Originally Posted by jwick

How much difficutly did you have removing the O2 sensor from the stock cats? It is possible you slightly damaged one and it took a few miles to completely fail.

After googling that code I see that it could be intake or exhaust leak or you could have a faulty senor. I don't think the loose coupler would cause that. I'd lean more to a bad sensor. Swap the two O2 sensor plugs and see if it changes banks.