Digital BW, The Print

Hi,
I make a linier gradient in ps 0-255 in adobe rgb document 8bit (16 
bit is not available), I have to get a print from my epson 820 
(6color printer).

I am getting serious banding effects within the range of 25-100 
approx, the 100-255 range prints perfectly, without banding.

My printer setup is 1440, microweave ON, photoEnhance , I have tried 
various combination & feel either its a printers limitation or some 
serious problem in my working setup, though I am making a file in 
adobe rgb which has quite wide gamut, I even tried in Wide gamut RGB, 
but the same problem.

Can any body share some thought to this problem.
Ranjan