Canon PRO-4000 and PRO-6000 both have ink starvation problem

[ukrsonic]

Hello,
we are getting soft banding on dark grey areas (Please see attached image).
I already did:
1. Firmware update;
2. Disassembled cover panels and checked for air bubbles;
3. Replaced print heads;
4. Increased Ink Dry time up to 3-9 sec;
5. Drilled holes in grey and black ink cartridges (so there is no vacuum);
6. Cleaned/washed with ultrasonic all purge pads.
7. Nozzle check, feed adjustment, head alignment;
All that didn't help.
We are having the same issue on both new printers((
Thank you for all your help in advance.

[ukrsonic]

Nope. And we got more problems from the imagePROGRAF series. Now we can't get perfect head alignment.
We are planning to get rid of these printers and replace them with older versions.