i have a 400ci that is having a rather weird issue if anyone can help. when you print with solid black everything looks fine but if you print with color towards the trail edge of the page you registration begins to separate. so the image goes from being nice and crisp to fuzzy and blurry on the trail edge. any suggestions? I've tried a new tr-belt, new drums, new developers, registration adjustments, and manual lsu registration adjustments.

Does the affect appear differently between copies and prints?

Two things that come to mind are:
1) that it's copies not prints, and that you have some sort of optical focus issue. You'll see that especially on the trailing edge of ledger/A3.
2) that if it affects both equally maybe you're fuser motor speed is not coordinated, specifically too fast, pulling the paper off the transfer belt.

change out transfer belt assy