Digital BW, The Print

I've been lurking here for a while - reading and learning - and am 
now in process of trying to get the best I can out of my Epson 
Stylus Photo 950.

I've read Clayton Jones' excellent papers on BW printing and I've 
been reasonably happy with the results I've got so far. I'm using 
Epson standard cartridges and Epson Archival Matt or Tetenal Premium 
Fine Art Glossy papers. A problem I've found is that I get quite 
distinct banding in detail-less neutral grey areas (e.g. skys) when 
I print at the Custom 2880dpi setting using BO. They are regular, 
and subtle, bands about 1cm wide with diffuse edges. If I use FI 
printing at the same setting I get no banding, just a denser print. 
No banding either using BO at the 1440 and 720dpi settings.

Does anyone have experience of this model Epson or can shed any 
light on a likely cause? I have two of these 950s and they both 
perform in exactly the same way - at least I have consistency!

Roy
http://www.weepingash.co.uk