5.7 hemi idle and backfire

Two co-incidental failures at the same time is highly unlikely.
I would be tempted to bolt those O2s back in and blame the problem on the plugs.You did replace the plugs too, right, as you said you would? I have seen it many times where sooted plugs leak away the spark and do other tricks on a running engine. Anyway it's only a few minutes to find out.But if you only replaced those O2s then skip over this paragraph.
COPs don't have the power characteristics to deal with sooted plugs. Furthermore COPS are usually designed for/around specific specialty plugs.They often have a hard time dealing with non-specialty plugs, with their higher voltage requirement for spark initiation..