Digital BW, The Print

I am experimenting with the R1800 3MK approach. At this time I have 
installed the full MIS R1800 color set but have used K4 for PK. I 
want to try both 3Mk and 3Pk as well as some MK and PK dilutions. 

However I have hit a snag from the get go. After many cleaning cycles 
I have finally got a good test pattern on all nozzles. However when 
printing a color image from PS I can see distinct banding in the 
shadow areas. It is very noticeable.

I then run QTR in calibration mode and I am seeing banding 
(horizontal) on all colors (incl MK and PK) from around 50% loading 
onwards.

I have undertaken a head alignment but no improvement.

Anyone have any suggestions for getting rid of banding with MIS inks 
or is my printer a dud? I see no point in going further with this 
approach on this particular printer unless I can resolve this.

All and any input appreciated!

regards

Alistair