The banding is its worst right after a power clean when printing a full, 100%, ink channel (one ink channel at 100% ink flow on 8.5"x11" paper... as described above). If I wait an hour or so after a power clean, the banding is greatly diminished. If I wait over night, I don't see any banding when printing a full, 100%, ink channel.
Since the problem is not persistent (goes away after some time has passed or I print an image), I'm not too concerned about it. I'll keep an eye on it. If it gets worse, I may opt to replace the dampers to see if that helps.
My current work around is to print one normal 8.5"x11" image using all ink channels right after a power clean. That first image will have banding but thereafter (2nd, 3rd, etc. images) there is no apparent banding.
Now that I have a second 7880, I will be dedicating ink sets to each printer and shouldn't need to perform any power cleans unless I have bad nozzle clogs which require power cleans or piezoflushing, or I need to switch ink sets.