Digital BW, The Print

Banding as illustrated in the 1160 's user manual has very distinct 
white lines - and if that's always the form it takes, then it's not 
what I have - what do I have ?

I just took delivery of a used 1160 and am running some basic tests 
while I wait for my quad inks and cis to arrive. Using the already 
installed 3rd party dye substitutes for OEM ink, and some 8.5x11 
Epson Photo Paper (gloss). 

I have run the Utility tab fixes for Nozzle Check & Clean, and the 
Head Allignment check/fix. Also the paper thickness lever is at 0. 

I first took a 21 step wedge (0 to 100%) with a narrow black to white 
gradient alongside it, and printed it on 6x4 inch Epson Photo Paper - 
all the steps printed clearly and the gradient looks smooth. So far 
so good.

I then opened a new file at 8.5x11 (at 360 dpi), and created a simple 
black to white gradient, to simulate a clear featureless expanse like 
a cloudless sky, and printed it twice - once in RGB mode and the 
other time the mode was changed to Greyscale (2.2 gamma for Win98).I 
did these 2 prints on Epson Photo Paper at the 1440 setting (actually 
printed it several times to see if there would be any change).

I observed slight "banding" or "whatever the problem may be called", 
in some areas and a little "horzontal texture":
On the RGB print -  
There is a distinct jump from white to tone somewhere between 0 and 5 
% (holding the little stepwedge alongside it). And again around 85 to 
90%.
The Greyscale print-
It generally looks a little better, but there is also a jump around 
5% and also around 95% and also at about 35 to 40%.

This "jump" or "stuttering" or "slightly abrupt" tonal change (not 
sure how to verbally describe it, is fairly subtle and if I were to 
scan it and post a link, I'm not sure it would be easily perceived.

Why would this be? And how should I interpret this result - is it 
cause for concern ? Is there a remedy I could try ? Obviously, few 
real world photos would contain such a featureless space as a black 
to white Photoshop gradient, but seems to make sense as a tonal 
transuition test.

Can I expect a totally smoth & textureless range from 0 to 100% ? Is 
it a limit of a 4 col printer ? Your experience would be appreciated.
thank you
Frank