Try to lock in position the lateral guides of the tray (with glue).
I have a Phaser 6600 DN that is printing "crooked". The output is rotated clockwise by about 2 degrees.
After putting a transfer belt maintenance kit in, the problem went from 3 degrees to 2 degrees.
This can be reproduced on multiple computers.
As well .. the effect is slightly less pronounced on a full tray compared to a mostly empty tray.
Thanks for your help in advance