Digital BW, The Print

Am getting beautiful results using an R1800 (Mac driven) with the 3MK
set up (thank you Paul) on Epson Enhanced Matte paper. Using only 3
Eboni cartridges, the rest contain clear base. No banding, "perfect"
prints.
When I print on Premier Art 325g Fine Art Hot Press or Premier Art
270g paper using Paul's profiles specific for these papers or
substituting the EEM profile I get horizontal banding in midtones. The
problem is the same whether the sheets are fed through the back or the
regular feed. The bands on the Premier paper are an issue in large
clear midtone areas like sky as they are subtle but clearly visible at
normal viewing distance. 
Nozzle checks are good. The problem is reproducible as one goes back
and forth between the EEM and Premier papers. 
Your thoughts on this are appreciated.
Thank you,
Harlan