Digital BW, The Print

I'm printing a series of pictures taken in ranch country with "big
skies". I'm finding that the tonal variation isn't printing as good as
I'd like it to. At 8x10 size, the tonal transitions in the sky look
somewhat "mottled".
The photos were raw images taken with a Canon 20D. Images were
processed with Photoshop Elements, printed with an Epson R220 and MIS
UT-R2 inks, and printed on both Epson Enhanced Matte and PremierArt
Hot Press. The effect seems to be a bit worse on the PremierArt paper.
It's difficult to tell (I need a better monitor), but I think the
effect is also seen on screen.
I'm trying to figure out what the likely culprit is. Could it be due
to working with 8 bit files in Elements instead of 16 bit files?
Tx.